diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -143,6 +143,7 @@
     'AphrontJavelinView' => 'view/AphrontJavelinView.php',
     'AphrontKeyboardShortcutsAvailableView' => 'view/widget/AphrontKeyboardShortcutsAvailableView.php',
     'AphrontListFilterView' => 'view/layout/AphrontListFilterView.php',
+    'AphrontMalformedRequestException' => 'aphront/exception/AphrontMalformedRequestException.php',
     'AphrontMoreView' => 'view/layout/AphrontMoreView.php',
     'AphrontMultiColumnView' => 'view/layout/AphrontMultiColumnView.php',
     'AphrontMySQLDatabaseConnectionTestCase' => 'infrastructure/storage/__tests__/AphrontMySQLDatabaseConnectionTestCase.php',
@@ -170,7 +171,6 @@
     'AphrontTokenizerTemplateView' => 'view/control/AphrontTokenizerTemplateView.php',
     'AphrontTypeaheadTemplateView' => 'view/control/AphrontTypeaheadTemplateView.php',
     'AphrontUnhandledExceptionResponse' => 'aphront/response/AphrontUnhandledExceptionResponse.php',
-    'AphrontUsageException' => 'aphront/exception/AphrontUsageException.php',
     'AphrontView' => 'view/AphrontView.php',
     'AphrontWebpageResponse' => 'aphront/response/AphrontWebpageResponse.php',
     'ArcanistConduitAPIMethod' => 'applications/arcanist/conduit/ArcanistConduitAPIMethod.php',
@@ -3771,6 +3771,7 @@
     'AphrontJavelinView' => 'AphrontView',
     'AphrontKeyboardShortcutsAvailableView' => 'AphrontView',
     'AphrontListFilterView' => 'AphrontView',
+    'AphrontMalformedRequestException' => 'AphrontException',
     'AphrontMoreView' => 'AphrontView',
     'AphrontMultiColumnView' => 'AphrontView',
     'AphrontMySQLDatabaseConnectionTestCase' => 'PhabricatorTestCase',
@@ -3800,7 +3801,6 @@
     'AphrontTokenizerTemplateView' => 'AphrontView',
     'AphrontTypeaheadTemplateView' => 'AphrontView',
     'AphrontUnhandledExceptionResponse' => 'AphrontStandaloneHTMLResponse',
-    'AphrontUsageException' => 'AphrontException',
     'AphrontView' => array(
       'Phobject',
       'PhutilSafeHTMLProducerInterface',
@@ -4383,7 +4383,7 @@
     'DiffusionSearchQueryConduitAPIMethod' => 'DiffusionQueryConduitAPIMethod',
     'DiffusionServeController' => 'DiffusionController',
     'DiffusionSetPasswordSettingsPanel' => 'PhabricatorSettingsPanel',
-    'DiffusionSetupException' => 'AphrontUsageException',
+    'DiffusionSetupException' => 'Exception',
     'DiffusionSubversionSSHWorkflow' => 'DiffusionSSHWorkflow',
     'DiffusionSubversionServeSSHWorkflow' => 'DiffusionSubversionSSHWorkflow',
     'DiffusionSubversionWireProtocol' => 'Phobject',
diff --git a/src/aphront/configuration/AphrontApplicationConfiguration.php b/src/aphront/configuration/AphrontApplicationConfiguration.php
--- a/src/aphront/configuration/AphrontApplicationConfiguration.php
+++ b/src/aphront/configuration/AphrontApplicationConfiguration.php
@@ -318,7 +318,7 @@
           // This is a command line script (probably something like a unit
           // test) so it's fine that we don't have SERVER_ADDR defined.
         } else {
-          throw new AphrontUsageException(
+          throw new AphrontMalformedRequestException(
             pht('No %s', 'SERVER_ADDR'),
             pht(
               'Phabricator is configured to operate in cluster mode, but '.
@@ -330,7 +330,7 @@
         }
       } else {
         if (!PhabricatorEnv::isClusterAddress($server_addr)) {
-          throw new AphrontUsageException(
+          throw new AphrontMalformedRequestException(
             pht('External Interface'),
             pht(
               'Phabricator is configured in cluster mode and the address '.
@@ -413,12 +413,14 @@
     if (!$site) {
       $path = $request->getPath();
       $host = $request->getHost();
-      throw new Exception(
+      throw new AphrontMalformedRequestException(
+        pht('Site Not Found'),
         pht(
           'This request asked for "%s" on host "%s", but no site is '.
           'configured which can serve this request.',
           $path,
-          $host));
+          $host),
+        true);
     }
 
     $request->setSite($site);
diff --git a/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php b/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
--- a/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
+++ b/src/aphront/configuration/AphrontDefaultApplicationConfiguration.php
@@ -210,22 +210,6 @@
       return $response;
     }
 
-    if ($ex instanceof AphrontUsageException) {
-      $error = new PHUIInfoView();
-      $error->setTitle($ex->getTitle());
-      $error->appendChild($ex->getMessage());
-
-      $view = new PhabricatorStandardPageView();
-      $view->setRequest($this->getRequest());
-      $view->appendChild($error);
-
-      $response = new AphrontWebpageResponse();
-      $response->setContent($view->render());
-      $response->setHTTPResponseCode(500);
-
-      return $response;
-    }
-
     // Always log the unhandled exception.
     phlog($ex);
 
diff --git a/src/aphront/exception/AphrontMalformedRequestException.php b/src/aphront/exception/AphrontMalformedRequestException.php
new file mode 100644
--- /dev/null
+++ b/src/aphront/exception/AphrontMalformedRequestException.php
@@ -0,0 +1,29 @@
+<?php
+
+/**
+ * These exceptions are raised when a client submits a malformed request.
+ *
+ * These errors are caught by Aphront itself and occur too early or too
+ * fundamentally in request handling to allow the request to route to a
+ * controller.
+ */
+final class AphrontMalformedRequestException extends AphrontException {
+
+  private $title;
+  private $silent;
+
+  public function __construct($title, $message, $silent = false) {
+    $this->title = $title;
+    $this->silent = $silent;
+    parent::__construct($message);
+  }
+
+  public function getTitle() {
+    return $this->title;
+  }
+
+  public function getSilent() {
+    return $this->silent;
+  }
+
+}
diff --git a/src/aphront/exception/AphrontUsageException.php b/src/aphront/exception/AphrontUsageException.php
deleted file mode 100644
--- a/src/aphront/exception/AphrontUsageException.php
+++ /dev/null
@@ -1,21 +0,0 @@
-<?php
-
-/**
- * These exceptions represent user error, and are not logged.
- *
- * @concrete-extensible
- */
-class AphrontUsageException extends AphrontException {
-
-  private $title;
-
-  public function __construct($title, $message) {
-    $this->title = $title;
-    parent::__construct($message);
-  }
-
-  public function getTitle() {
-    return $this->title;
-  }
-
-}
diff --git a/src/aphront/response/AphrontUnhandledExceptionResponse.php b/src/aphront/response/AphrontUnhandledExceptionResponse.php
--- a/src/aphront/response/AphrontUnhandledExceptionResponse.php
+++ b/src/aphront/response/AphrontUnhandledExceptionResponse.php
@@ -24,7 +24,7 @@
   protected function getResponseTitle() {
     $ex = $this->exception;
 
-    if ($ex instanceof AphrontUsageException) {
+    if ($ex instanceof AphrontMalformedRequestException) {
       return $ex->getTitle();
     } else {
       return pht('Unhandled Exception');
@@ -38,7 +38,7 @@
   protected function getResponseBody() {
     $ex = $this->exception;
 
-    if ($ex instanceof AphrontUsageException) {
+    if ($ex instanceof AphrontMalformedRequestException) {
       $title = $ex->getTitle();
     } else {
       $title = get_class($ex);
diff --git a/src/applications/diffusion/exception/DiffusionSetupException.php b/src/applications/diffusion/exception/DiffusionSetupException.php
--- a/src/applications/diffusion/exception/DiffusionSetupException.php
+++ b/src/applications/diffusion/exception/DiffusionSetupException.php
@@ -1,9 +1,3 @@
 <?php
 
-final class DiffusionSetupException extends AphrontUsageException {
-
-  public function __construct($message) {
-    parent::__construct(pht('Diffusion Setup Exception'), $message);
-  }
-
-}
+final class DiffusionSetupException extends Exception {}