I needed to install mcrypt on Mac OS X Mavericks 10.9 for installing the Laravel 5 framework. I entered in the Terminal command line:
brew tap josegonzalez/homebrew-php
brew install php54 php54-mcrypt
This installed Mcrypt. In Terminal type php -i to see a list of everything installed or for much better formatting and easier to read make a phpinfo.php page with this inside <?php phpinfo(); ?>
More help with installing on OS X:
http://stackoverflow.com/questions/14595841/installing-mcrypt-extension-for-php-on-osx-mountain-lion