diff --git a/src/applications/config/check/PhabricatorMySQLSetupCheck.php b/src/applications/config/check/PhabricatorMySQLSetupCheck.php
--- a/src/applications/config/check/PhabricatorMySQLSetupCheck.php
+++ b/src/applications/config/check/PhabricatorMySQLSetupCheck.php
@@ -44,6 +44,40 @@
         ->addMySQLConfig('max_allowed_packet');
     }
 
+    $max_connections = self::loadRawConfigValue('max_connections');
+
+    // A common default is 150, but we're fairly liberal about the number of
+    // connections we open and it's easy for us to run far over this limit.
+
+    $warning_threshold = 256;
+    if ($max_connections < $warning_threshold) {
+      $message = pht(
+        'MySQL is configured with a small "%s" (%d) limit, which may cause '.
+        'connection failures long before any resources near exhaustion. '.
+        'There is normally very little benefit to enforcing a connection '.
+        'limit, and most installs should increase it substantially.'.
+        "\n\n".
+        'You can compute a specific connection limit for your install by '.
+        'doing a lot of math with MySQL buffer sizes and RAM available on '.
+        'the machine, or just set it to a huge number. In nearly every case, '.
+        'setting it to a huge number is entirely reasonable.'.
+        "\n\n".
+        'You can raise this limit by adding this to your %s file (in the %s '.
+        'section) and then restarting %s:'.
+        "\n\n%s",
+        'max_connections',
+        $max_connections,
+        phutil_tag('tt', array(), 'my.cnf'),
+        phutil_tag('tt', array(), '[mysqld]'),
+        phutil_tag('tt', array(), 'mysqld'),
+        phutil_tag('pre', array(), 'max_connections=100000'));
+
+      $this->newIssue('mysql.max_connections')
+        ->setName(pht('Small MySQL "%s"', 'max_connections'))
+        ->setMessage($message)
+        ->addMySQLConfig('max_connections');
+    }
+
     $modes = self::loadRawConfigValue('sql_mode');
     $modes = explode(',', $modes);