diff --git a/mkdocs/structure/files.py b/mkdocs/structure/files.py
index cc2d25b9..dbef68a5 100644
--- a/mkdocs/structure/files.py
+++ b/mkdocs/structure/files.py
@@ -38,6 +38,7 @@ class Files:
     def __init__(self, files: List[File]) -> None:
         self._files = files
         self._src_uris: Optional[Dict[str, File]] = None
+        self._documentation_pages: Optional[Sequence[File]] = None
 
     def __iter__(self) -> Iterator[File]:
         """Iterate over the files within."""
@@ -70,12 +71,12 @@ class Files:
 
     def append(self, file: File) -> None:
         """Append file to Files collection."""
-        self._src_uris = None
+        self._src_uris = self._documentation_pages = None
         self._files.append(file)
 
     def remove(self, file: File) -> None:
         """Remove file from Files collection."""
-        self._src_uris = None
+        self._src_uris = self._documentation_pages = None
         self._files.remove(file)
 
     def copy_static_files(self, dirty: bool = False) -> None:
@@ -86,7 +87,9 @@ class Files:
 
     def documentation_pages(self) -> Sequence[File]:
         """Return iterable of all Markdown page file objects."""
-        return [file for file in self if file.is_documentation_page()]
+        if self._documentation_pages is None:
+            self._documentation_pages = [file for file in self if file.is_documentation_page()]
+        return self._documentation_pages
 
     def static_pages(self) -> Sequence[File]:
         """Return iterable of all static page file objects."""
diff --git a/mkdocs/tests/structure/file_tests.py b/mkdocs/tests/structure/file_tests.py
index 51030e1f..fb13bd06 100644
--- a/mkdocs/tests/structure/file_tests.py
+++ b/mkdocs/tests/structure/file_tests.py
@@ -380,13 +380,14 @@ class TestFiles(PathAssertionMixin, unittest.TestCase):
         self.assertEqual(files.get_file_from_path('foo/bar.jpg'), fs[3])
         self.assertEqual(files.get_file_from_path('missing.jpg'), None)
         self.assertTrue(fs[2].src_uri in files.src_uris)
-        self.assertTrue(fs[2].src_uri in files.src_uris)
         extra_file = File('extra.md', '/path/to/docs', '/path/to/site', use_directory_urls=True)
         self.assertFalse(extra_file.src_uri in files.src_uris)
         files.append(extra_file)
         self.assertEqual(len(files), 7)
         self.assertTrue(extra_file.src_uri in files.src_uris)
         self.assertEqual(files.documentation_pages(), [fs[0], fs[1], extra_file])
+        files.remove(fs[1])
+        self.assertEqual(files.documentation_pages(), [fs[0], extra_file])
 
     @tempdir(
         files=[