diff --git a/doc/api/next_api_changes/2018-08-17-AL-deprecations.rst b/doc/api/next_api_changes/2018-08-17-AL-deprecations.rst
index 4097437b3c08..f03163baff33 100644
--- a/doc/api/next_api_changes/2018-08-17-AL-deprecations.rst
+++ b/doc/api/next_api_changes/2018-08-17-AL-deprecations.rst
@@ -7,3 +7,6 @@ The following API elements are deprecated:
 - ``backend_ps.PsBackendHelper``, ``backend_ps.ps_backend_helper``,
 - ``cbook.iterable``,
 - ``mlab.demean``,
+
+The following environment variables are deprecated:
+- ``MATPLOTLIBDATA``,
diff --git a/lib/matplotlib/__init__.py b/lib/matplotlib/__init__.py
index d5cf4d3d99fe..e339b7c8aa4e 100644
--- a/lib/matplotlib/__init__.py
+++ b/lib/matplotlib/__init__.py
@@ -652,6 +652,8 @@ def _get_data_path():
         if not os.path.isdir(path):
             raise RuntimeError('Path in environment MATPLOTLIBDATA not a '
                                'directory')
+        cbook.warn_deprecated(
+            "3.1", name="MATPLOTLIBDATA", obj_type="environment variable")
         return path
 
     def get_candidate_paths():