Obsessive-compulsive disorder
Obsessive-compulsive disorder is defined as the presence of obsessions or compulsions that produce substantial discomfort or impairment.
Obsessions are recurrent, markedly distressing thoughts, ideas, or impulses experienced as unwanted and senseless. Compulsions are repetitive, purposeful, intentional behaviors, usually performed in response to an obsession in order to reduce the distress or prevent some dreaded event.
(Source: DSM-IV)