The worldwide prevalence of obsessive-compulsive disorder (OCD) is approximately 2% of the general population. Symptoms of OCD include fear of contamination by dirt or germs; constant checking; repetitive, intrusive thoughts of a somatic, aggressive, or sexual nature; extreme slowness; and an inordinate concern with orderliness and symmetry. Differential diagnosis is sometimes complicated by the overlap between OCD and obsessive-compulsive personality disorder (OCPD). The most common complication of OCD is depression. However, while both serotonergic and nonserotonergic antidepressants are effective in treating patients with depression, only serotonergic medications are effective in treating OCD patients. Because OCD patients often attempt to conceal their symptoms, it is incumbent on clinicians to screen for OCD in every mental status examination, since appropriate treatment can often result in improved quality of life.