Obsessive-compulsive disorder is defined by Mayo Clinic as a psychiatric disorder in which a person experiences repeated thoughts, or obsessions, and partakes in repeated behaviors, often to relieve the thoughts, or compulsions. Common obsessions include obsessions about hygiene, orderliness, violent thoughts, sexual thoughts or blasphemous thoughts. Compulsions are sometimes related to the obsessions; ritualistic hand-washing is an example of a compulsion related to a hygiene obsession.
Wikipedia states that obsessive-compulsive disorder is an anxiety disorder, and that obsessions are often in the form of intrusive thoughts. Intrusive thoughts are unwanted thoughts that cause the patient to feel distressed. Both obsessions and compulsive behaviors are not necessarily present in all patients suffering from obsessive-compulsive disorder. Some patients experience only obsessions, while other only experience compulsions. Wikipedia also notes that patients who suffer from obsessive-compulsive disorder often have a high verbal IQ.
The National Institute of Mental Health states that there is a genetic factor involved in obsessive-compulsive disorder, however it is unknown why some family members develop the disorder while others do not. Some common compulsions exhibited by obsessive-compulsive patients include counting, repetitive checking, repetitive hand-washing and hoarding. Severe obsessive-compulsive disorder conflicts with patients' daily lives and often becomes distressful and unmanageable. Before a doctor diagnoses a patient with obsessive-compulsive disorder, he often performs a medical exam to rule out a physiological cause of the symptoms.