diff --git nodeapi_example/nodeapi_example.install nodeapi_example/nodeapi_example.install
index d470be8..4b64bff 100644
--- nodeapi_example/nodeapi_example.install
+++ nodeapi_example/nodeapi_example.install
@@ -17,8 +17,25 @@ function nodeapi_example_install() {
 
 /**
  * Implements hook_uninstall().
+ *
+ * We need to cleanup our data when uninstalling
+ * our module.
  */
 function nodeapi_example_uninstall() {
+
+  // Delete the nodeapi module variables because we don't need them anymore.
+  // Our implementation of nodeapi_example_form_alter() automatically
+  // created a nodeapi_example_contentType variable
+  // for each contenttype in the variable table.
+  // This means we need to delete the variables when uninstalling
+  // the module.
+
+  $availableContentTypes = node_type_get_types();
+  $availableContentTypes = array_keys($availableContentTypes);
+
+  foreach($availableContentTypes as $contentType) {
+    variable_del('nodeapi_example_' . $contentType);
+  }
 }
 
 /**