Recurring unwanted and intrusive thoughts (obsessions) and repetitive senseless behaviors or rituals (compulsions) characterize obsessive-compulsive disorder. Compulsions usually occur in response to the anxiety-provoking obsessions, and in an attempt to alleviate the anxiety, can themselves become extremely distressing and time-consuming. Compulsions may also manifest as mental rituals done in one’s mind, rather than external behaviors. For instance, counting sequences in one’s head may reduce anxiety produced by unwanted thoughts. Please visit the Obsessive-Compulsive Disorder Foundation for further information.