Obsessive-compulsive disorder (OCD) is a chronic and often disabling disease. OCD is characterised by intrusive, unwanted and persistently recurring mental events (obsessions) that usually evoke discomfort or anxiety, and/or repetitive ritualistic behaviours (compulsions) that are aimed at reducing discomfort and anxiety. However, the compulsions succeed only in achieving transient relief, followed by a growing sense of pressure. 10 years ago, OCD was considered a rare and treatment-refractory disorder. Recent well de-signed studies document a lifetime prevalence rate for OCD of more than 2% in the general population. The outlook for patients with OCD has changed in the last decade, with many well controlled studies showing that OCD patients respond to specific behavioural and pharmacological treatments. The specific form of behavioural therapy is in vivo exposure coupled with response prevention. Only serotonin reuptake inhibitors, such as clomipramine, fluoxetine and fluvoxamine, are effective in the treatment of both depressed and not depressed OCD patients. Fluoxetine and fluvoxamine lack the anticholinergic side effects of clomipramine and, thus, provide an alternative treatment for patients who cannot tolerate clomipramine. Other nonserotonergic antidepressants (tricyclics and monoamine oxidase inhibitors) and anxiolytic agents have not been found to be consistently effective in this disorder. Insufficient data on the efficacy of neuroleptics and their potentially irreversible side effects limit their use in OCD patients. Behavioural and the pharmacological treatment are complementary, and a combination of the 2 therapies is apparently more effective than either modality alone.