diff --git a/src/applications/phriction/editor/PhrictionTransactionEditor.php b/src/applications/phriction/editor/PhrictionTransactionEditor.php
--- a/src/applications/phriction/editor/PhrictionTransactionEditor.php
+++ b/src/applications/phriction/editor/PhrictionTransactionEditor.php
@@ -3,6 +3,9 @@
 final class PhrictionTransactionEditor
   extends PhabricatorApplicationTransactionEditor {
 
+  const VALIDATE_CREATE_ANCESTRY = 'create';
+  const VALIDATE_MOVE_ANCESTRY   = 'move';
+
   private $description;
   private $oldContent;
   private $newContent;
@@ -519,6 +522,18 @@
               $errors[] = $error;
             }
           }
+
+          if ($this->getIsNewObject()) {
+            $ancestry_errors = $this->validateAncestry(
+              $object,
+              $type,
+              $xaction,
+              self::VALIDATE_CREATE_ANCESTRY);
+            if ($ancestry_errors) {
+              $errors = array_merge($errors, $ancestry_errors);
+            }
+          }
+
           break;
 
         case PhrictionTransaction::TYPE_MOVE_TO:
@@ -547,8 +562,15 @@
             $errors[] = $error;
           }
 
-          // NOTE: We use the ominpotent user because we can't let users
-          // overwrite documents even if they can't see them.
+          $ancestry_errors = $this->validateAncestry(
+            $object,
+            $type,
+            $xaction,
+            self::VALIDATE_MOVE_ANCESTRY);
+          if ($ancestry_errors) {
+            $errors = array_merge($errors, $ancestry_errors);
+          }
+
           $target_document = id(new PhrictionDocumentQuery())
             ->setViewer(PhabricatorUser::getOmnipotentUser())
             ->withSlugs(array($object->getSlug()))
@@ -606,6 +628,59 @@
     return $errors;
   }
 
+  private function validateAncestry(
+    PhabricatorLiskDAO $object,
+    $type,
+    PhabricatorApplicationTransaction $xaction,
+    $verb) {
+
+    $errors = array();
+    // NOTE: We use the ominpotent user for these checks because policy
+    // doesn't matter; existence does.
+    $other_doc_viewer = PhabricatorUser::getOmnipotentUser();
+    $ancestral_slugs = PhabricatorSlug::getAncestry($object->getSlug());
+    if ($ancestral_slugs) {
+      $ancestors = id(new PhrictionDocumentQuery())
+        ->setViewer($other_doc_viewer)
+        ->withSlugs($ancestral_slugs)
+        ->execute();
+      $ancestors = mpull($ancestors, null, 'getSlug');
+      foreach ($ancestral_slugs as $slug) {
+        $ancestor_doc = idx($ancestors, $slug);
+        if (!$ancestor_doc) {
+          $create_uri = '/phriction/edit/?slug='.$slug;
+          $create_link = phutil_tag(
+            'a',
+            array(
+              'href' => $create_uri,
+            ),
+            $slug);
+          switch ($verb) {
+            case self::VALIDATE_MOVE_ANCESTRY:
+              $message = pht(
+                'Can not move document because the parent document with '.
+                'slug %s does not exist!',
+                $create_link);
+              break;
+            case self::VALIDATE_CREATE_ANCESTRY:
+              $message = pht(
+                'Can not create document because the parent document with '.
+                'slug %s does not exist!',
+                $create_link);
+              break;
+          }
+          $error = new PhabricatorApplicationTransactionValidationError(
+            $type,
+            pht('Missing Ancestor'),
+            $message,
+            $xaction);
+          $errors[] = $error;
+        }
+      }
+    }
+    return $errors;
+  }
+
   private function validateContentVersion(
     PhabricatorLiskDAO $object,
     $type,