diff --git a/doc/source/user_guide/io.rst b/doc/source/user_guide/io.rst
index 7caaec62c0a8a..6b3edd92ab5a9 100644
--- a/doc/source/user_guide/io.rst
+++ b/doc/source/user_guide/io.rst
@@ -3319,16 +3319,7 @@ any pickled pandas object (or any other pickled object) from file:
 
 .. warning::
 
-   Several internal refactoring have been done while still preserving
-   compatibility with pickles created with older versions of pandas. However,
-   for such cases, pickled ``DataFrames``, ``Series`` etc, must be read with
-   ``pd.read_pickle``, rather than ``pickle.load``.
-
-   See `here <https://pandas.pydata.org/pandas-docs/stable/whatsnew.html#whatsnew-0130-refactoring>`__
-   and `here <https://pandas.pydata.org/pandas-docs/stable/whatsnew.html#whatsnew-0150-refactoring>`__
-   for some examples of compatibility-breaking changes. See
-   `this question <https://stackoverflow.com/questions/20444593/pandas-compiled-from-source-default-pickle-behavior-changed>`__
-   for a detailed explanation.
+   :func:`read_pickle` is only guaranteed backwards compatible back to pandas version 0.20.3
 
 .. _io.pickle.compression:
 
@@ -3406,6 +3397,10 @@ both on the writing (serialization), and reading (deserialization).
    optimizations in the io of the ``msgpack`` data. Since this is marked
    as an EXPERIMENTAL LIBRARY, the storage format may not be stable until a future release.
 
+.. warning::
+
+   :func:`read_msgpack` is only guaranteed backwards compatible back to pandas version 0.20.3
+
 .. ipython:: python
 
    df = pd.DataFrame(np.random.rand(5, 2), columns=list('AB'))
diff --git a/doc/source/whatsnew/v0.25.0.rst b/doc/source/whatsnew/v0.25.0.rst
index 0853a5962272a..d47b97d8a331d 100644
--- a/doc/source/whatsnew/v0.25.0.rst
+++ b/doc/source/whatsnew/v0.25.0.rst
@@ -13,6 +13,11 @@ What's New in 0.25.0 (April XX, 2019)
    `Panel` has been fully removed. For N-D labeled data structures, please
    use `xarray <https://xarray.pydata.org/en/stable/>`_
 
+.. warning::
+
+   :func:`read_pickle` and :func:`read_msgpack` are only guaranteed backwards compatible back to
+   pandas version 0.20.3 (:issue:`27082`)
+
 {{ header }}
 
 These are the changes in pandas 0.25.0. See :ref:`release` for a full changelog
diff --git a/pandas/io/packers.py b/pandas/io/packers.py
index e3d45548e4978..4a273bfe2decb 100644
--- a/pandas/io/packers.py
+++ b/pandas/io/packers.py
@@ -134,6 +134,11 @@ def read_msgpack(path_or_buf, encoding='utf-8', iterator=False, **kwargs):
     Returns
     -------
     obj : same type as object stored in file
+
+    Notes
+    -----
+    read_msgpack is only guaranteed to be backwards compatible to pandas
+    0.20.3.
     """
     path_or_buf, _, _, should_close = get_filepath_or_buffer(path_or_buf)
     if iterator:
diff --git a/pandas/io/pickle.py b/pandas/io/pickle.py
index ce2ed247c158b..afe1622d99eac 100644
--- a/pandas/io/pickle.py
+++ b/pandas/io/pickle.py
@@ -116,6 +116,10 @@ def read_pickle(path, compression='infer'):
     read_sql : Read SQL query or database table into a DataFrame.
     read_parquet : Load a parquet object, returning a DataFrame.
 
+    Notes
+    -----
+    read_pickle is only guaranteed to be backwards compatible to pandas 0.20.3.
+
     Examples
     --------
     >>> original_df = pd.DataFrame({"foo": range(5), "bar": range(5, 10)})
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similarity index 85%
rename from pandas/tests/io/data/legacy_pickle/0.18.1/0.18.1_x86_64_darwin_3.5.2.pickle
rename to pandas/tests/io/data/legacy_pickle/0.20.3/0.20.3_x86_64_darwin_3.5.2.pickle
index 20af597c57a1b..9777319465de6 100644
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diff --git a/pandas/tests/io/generate_legacy_storage_files.py b/pandas/tests/io/generate_legacy_storage_files.py
index a4242ad18411b..5bb7fe8e6367d 100755
--- a/pandas/tests/io/generate_legacy_storage_files.py
+++ b/pandas/tests/io/generate_legacy_storage_files.py
@@ -4,10 +4,10 @@
 self-contained to write legacy storage (pickle/msgpack) files
 
 To use this script. Create an environment where you want
-generate pickles, say its for 0.18.1, with your pandas clone
+generate pickles, say its for 0.20.3, with your pandas clone
 in ~/pandas
 
-. activate pandas_0.18.1
+. activate pandas_0.20.3
 cd ~/
 
 $ python pandas/pandas/tests/io/generate_legacy_storage_files.py \
@@ -15,10 +15,10 @@
 
 This script generates a storage file for the current arch, system,
 and python version
-  pandas version: 0.18.1
+  pandas version: 0.20.3
   output dir    : pandas/pandas/tests/io/data/legacy_pickle/0.18.1/
   storage format: pickle
-created pickle file: 0.18.1_x86_64_darwin_3.5.2.pickle
+created pickle file: 0.20.3_x86_64_darwin_3.5.2.pickle
 
 The idea here is you are using the *current* version of the
 generate_legacy_storage_files with an *older* version of pandas to
@@ -45,7 +45,7 @@
 
 import pandas
 from pandas import (
-    Categorical, DataFrame, Index, MultiIndex, NaT, Period, Series,
+    Categorical, DataFrame, Index, MultiIndex, NaT, Period, RangeIndex, Series,
     SparseDataFrame, SparseSeries, Timestamp, bdate_range, date_range,
     period_range, timedelta_range, to_msgpack)
 
@@ -118,9 +118,7 @@ def create_data():
                  uint=Index(np.arange(10, dtype=np.uint64)),
                  timedelta=timedelta_range('00:00:00', freq='30T', periods=10))
 
-    if _loose_version >= LooseVersion('0.18'):
-        from pandas import RangeIndex
-        index['range'] = RangeIndex(10)
+    index['range'] = RangeIndex(10)
 
     if _loose_version >= LooseVersion('0.21'):
         from pandas import interval_range
@@ -191,14 +189,9 @@ def create_data():
                      nat=NaT,
                      tz=Timestamp('2011-01-01', tz='US/Eastern'))
 
-    if _loose_version < LooseVersion('0.19.2'):
-        timestamp['freq'] = Timestamp('2011-01-01', offset='D')
-        timestamp['both'] = Timestamp('2011-01-01', tz='Asia/Tokyo',
-                                      offset='M')
-    else:
-        timestamp['freq'] = Timestamp('2011-01-01', freq='D')
-        timestamp['both'] = Timestamp('2011-01-01', tz='Asia/Tokyo',
-                                      freq='M')
+    timestamp['freq'] = Timestamp('2011-01-01', freq='D')
+    timestamp['both'] = Timestamp('2011-01-01', tz='Asia/Tokyo',
+                                  freq='M')
 
     off = {'DateOffset': DateOffset(years=1),
            'DateOffset_h_ns': DateOffset(hour=6, nanoseconds=5824),
@@ -239,14 +232,6 @@ def create_data():
 def create_pickle_data():
     data = create_data()
 
-    # Pre-0.14.1 versions generated non-unpicklable mixed-type frames and
-    # panels if their columns/items were non-unique.
-    if _loose_version < LooseVersion('0.14.1'):
-        del data['frame']['mixed_dup']
-        del data['panel']['mixed_dup']
-    if _loose_version < LooseVersion('0.17.0'):
-        del data['series']['period']
-        del data['scalars']['period']
     return data
 
 
@@ -256,14 +241,6 @@ def _u(x):
 
 def create_msgpack_data():
     data = create_data()
-    if _loose_version < LooseVersion('0.17.0'):
-        del data['frame']['mixed_dup']
-        del data['panel']['mixed_dup']
-        del data['frame']['dup']
-        del data['panel']['dup']
-    if _loose_version < LooseVersion('0.18.0'):
-        del data['series']['dt_tz']
-        del data['frame']['dt_mixed_tzs']
     # Not supported
     del data['sp_series']
     del data['sp_frame']
@@ -272,7 +249,8 @@ def create_msgpack_data():
     del data['frame']['cat_onecol']
     del data['frame']['cat_and_float']
     del data['scalars']['period']
-    if _loose_version < LooseVersion('0.23.0'):
+    if _loose_version >= LooseVersion('0.21') and (
+            _loose_version < LooseVersion('0.23.0')):
         del data['index']['interval']
     del data['offsets']
     return _u(data)
@@ -285,7 +263,6 @@ def platform_name():
 
 def write_legacy_pickles(output_dir):
 
-    # make sure we are < 0.13 compat (in py3)
     version = pandas.__version__
 
     print("This script generates a storage file for the current arch, system, "
diff --git a/pandas/tests/io/test_packers.py b/pandas/tests/io/test_packers.py
index 9337d5916acc6..59fa9fbd02da1 100644
--- a/pandas/tests/io/test_packers.py
+++ b/pandas/tests/io/test_packers.py
@@ -1,5 +1,4 @@
 import datetime
-from distutils.version import LooseVersion
 import glob
 from io import BytesIO
 import os
@@ -84,7 +83,6 @@ def check_arbitrary(a, b):
         assert(a == b)
 
 
-@pytest.mark.filterwarnings("ignore:\\nPanel:FutureWarning")
 class TestPackers:
 
     def setup_method(self, method):
@@ -99,7 +97,6 @@ def encode_decode(self, x, compress=None, **kwargs):
             return read_msgpack(p, **kwargs)
 
 
-@pytest.mark.filterwarnings("ignore:\\nPanel:FutureWarning")
 class TestAPI(TestPackers):
 
     def test_string_io(self):
@@ -463,7 +460,6 @@ def test_basic(self):
                 assert_categorical_equal(i, i_rec)
 
 
-@pytest.mark.filterwarnings("ignore:\\nPanel:FutureWarning")
 class TestNDFrame(TestPackers):
 
     def setup_method(self, method):
@@ -842,7 +838,6 @@ def legacy_packer(request, datapath):
     return datapath(request.param)
 
 
-@pytest.mark.filterwarnings("ignore:\\nPanel:FutureWarning")
 @pytest.mark.filterwarnings("ignore:Sparse:FutureWarning")
 class TestMsgpack:
     """
@@ -858,15 +853,11 @@ class TestMsgpack:
     minimum_structure = {'series': ['float', 'int', 'mixed',
                                     'ts', 'mi', 'dup'],
                          'frame': ['float', 'int', 'mixed', 'mi'],
-                         'panel': ['float'],
                          'index': ['int', 'date', 'period'],
                          'mi': ['reg2']}
 
     def check_min_structure(self, data, version):
         for typ, v in self.minimum_structure.items():
-            if typ == "panel":
-                # FIXME: kludge; get this key out of the legacy file
-                continue
 
             assert typ in data, '"{0}" not found in unpacked data'.format(typ)
             for kind in v:
@@ -874,15 +865,7 @@ def check_min_structure(self, data, version):
                 assert kind in data[typ], msg
 
     def compare(self, current_data, all_data, vf, version):
-        # GH12277 encoding default used to be latin-1, now utf-8
-        if LooseVersion(version) < LooseVersion('0.18.0'):
-            data = read_msgpack(vf, encoding='latin-1')
-        else:
-            data = read_msgpack(vf)
-
-        if "panel" in data:
-            # FIXME: kludge; get the key out of the stored file
-            del data["panel"]
+        data = read_msgpack(vf)
 
         self.check_min_structure(data, version)
         for typ, dv in data.items():
@@ -909,33 +892,16 @@ def compare(self, current_data, all_data, vf, version):
         return data
 
     def compare_series_dt_tz(self, result, expected, typ, version):
-        # 8260
-        # dtype is object < 0.17.0
-        if LooseVersion(version) < LooseVersion('0.17.0'):
-            expected = expected.astype(object)
-            tm.assert_series_equal(result, expected)
-        else:
-            tm.assert_series_equal(result, expected)
+        tm.assert_series_equal(result, expected)
 
     def compare_frame_dt_mixed_tzs(self, result, expected, typ, version):
-        # 8260
-        # dtype is object < 0.17.0
-        if LooseVersion(version) < LooseVersion('0.17.0'):
-            expected = expected.astype(object)
-            tm.assert_frame_equal(result, expected)
-        else:
-            tm.assert_frame_equal(result, expected)
+        tm.assert_frame_equal(result, expected)
 
     def test_msgpacks_legacy(self, current_packers_data, all_packers_data,
                              legacy_packer, datapath):
 
         version = os.path.basename(os.path.dirname(legacy_packer))
 
-        # GH12142 0.17 files packed in P2 can't be read in P3
-        if (version.startswith('0.17.') and
-                legacy_packer.split('.')[-4][-1] == '2'):
-            msg = "Files packed in Py2 can't be read in Py3 ({})"
-            pytest.skip(msg.format(version))
         try:
             with catch_warnings(record=True):
                 self.compare(current_packers_data, all_packers_data,
diff --git a/pandas/tests/io/test_pickle.py b/pandas/tests/io/test_pickle.py
index b115a08d3b0d3..eb912908d28f4 100644
--- a/pandas/tests/io/test_pickle.py
+++ b/pandas/tests/io/test_pickle.py
@@ -11,7 +11,6 @@
 3. Move the created pickle to "data/legacy_pickle/<version>" directory.
 """
 import bz2
-from distutils.version import LooseVersion
 import glob
 import gzip
 import lzma
@@ -69,18 +68,8 @@ def compare(data, vf, version):
 
     m = globals()
     for typ, dv in data.items():
-        if typ == "panel":
-            # FIXME: kludge; get this key out of the legacy file
-            continue
-
         for dt, result in dv.items():
-            try:
-                expected = data[typ][dt]
-            except (KeyError):
-                if version in ('0.10.1', '0.11.0') and dt == 'reg':
-                    break
-                else:
-                    raise
+            expected = data[typ][dt]
 
             # use a specific comparator
             # if available
@@ -92,12 +81,7 @@ def compare(data, vf, version):
 
 
 def compare_sp_series_ts(res, exp, typ, version):
-    # SparseTimeSeries integrated into SparseSeries in 0.12.0
-    # and deprecated in 0.17.0
-    if version and LooseVersion(version) <= LooseVersion("0.12.0"):
-        tm.assert_sp_series_equal(res, exp, check_series_type=False)
-    else:
-        tm.assert_sp_series_equal(res, exp)
+    tm.assert_sp_series_equal(res, exp)
 
 
 def compare_series_ts(result, expected, typ, version):
@@ -121,47 +105,19 @@ def compare_series_ts(result, expected, typ, version):
 
 
 def compare_series_dt_tz(result, expected, typ, version):
-    # 8260
-    # dtype is object < 0.17.0
-    if LooseVersion(version) < LooseVersion('0.17.0'):
-        expected = expected.astype(object)
-        tm.assert_series_equal(result, expected)
-    else:
-        tm.assert_series_equal(result, expected)
+    tm.assert_series_equal(result, expected)
 
 
 def compare_series_cat(result, expected, typ, version):
-    # Categorical dtype is added in 0.15.0
-    # ordered is changed in 0.16.0
-    if LooseVersion(version) < LooseVersion('0.15.0'):
-        tm.assert_series_equal(result, expected, check_dtype=False,
-                               check_categorical=False)
-    elif LooseVersion(version) < LooseVersion('0.16.0'):
-        tm.assert_series_equal(result, expected, check_categorical=False)
-    else:
-        tm.assert_series_equal(result, expected)
+    tm.assert_series_equal(result, expected)
 
 
 def compare_frame_dt_mixed_tzs(result, expected, typ, version):
-    # 8260
-    # dtype is object < 0.17.0
-    if LooseVersion(version) < LooseVersion('0.17.0'):
-        expected = expected.astype(object)
-        tm.assert_frame_equal(result, expected)
-    else:
-        tm.assert_frame_equal(result, expected)
+    tm.assert_frame_equal(result, expected)
 
 
 def compare_frame_cat_onecol(result, expected, typ, version):
-    # Categorical dtype is added in 0.15.0
-    # ordered is changed in 0.16.0
-    if LooseVersion(version) < LooseVersion('0.15.0'):
-        tm.assert_frame_equal(result, expected, check_dtype=False,
-                              check_categorical=False)
-    elif LooseVersion(version) < LooseVersion('0.16.0'):
-        tm.assert_frame_equal(result, expected, check_categorical=False)
-    else:
-        tm.assert_frame_equal(result, expected)
+    tm.assert_frame_equal(result, expected)
 
 
 def compare_frame_cat_and_float(result, expected, typ, version):
@@ -177,11 +133,7 @@ def compare_index_period(result, expected, typ, version):
 
 
 def compare_sp_frame_float(result, expected, typ, version):
-    if LooseVersion(version) <= LooseVersion('0.18.1'):
-        tm.assert_sp_frame_equal(result, expected, exact_indices=False,
-                                 check_dtype=False)
-    else:
-        tm.assert_sp_frame_equal(result, expected)
+    tm.assert_sp_frame_equal(result, expected)
 
 
 files = glob.glob(os.path.join(os.path.dirname(__file__), "data",