Obsessive-compulsive disorder:

disorder characterize by obsessive thinking and/or compulsive behavior. The behavior may involve repetitive practices (e.g. hand-washing), which are undertaken with the belief they will allow the individual to reduce the anxiety caused by obsessive thoughts (perhaps by allowing the individual to avoid some feared outcome around with the thoughts revolve). Although many associate obsessive-compulsive disorder, or OCD, with these ritualistic behaviors, an OCD diagnosis does not require compulsive behavior; intrusive and obsessive thoughts can be sufficient for an OCD diagnosis.