Obsessive-compulsive disorder is a severe and disabling clinical condition that usually arises in late adolescence or
early adulthood and, if left untreated, has a chronic course. Whether this disorder should be classifi ed as an anxiety
disorder or in a group of putative obsessive-compulsive-related disorders is still a matter of debate. Biological models
of obsessive-compulsive disorder propose anomalies in the serotonin pathway and dysfunctional circuits in the
orbito-striatal area and dorsolateral prefrontal cortex. Support for these models is mixed and they do not account for
the symptomatic heterogeneity of the disorder. The cognitive-behavioural model of obsessive-compulsive disorder,
which has some empirical support but does not fully explain the disorder, emphasises the importance of dysfunctional
beliefs in individuals aff ected. Both biological and cognitive models have led to empirical treatments for the
disorder—ie, serotonin-reuptake inhibitors and various forms of cognitive-behavioural therapy. New developments in
the treatment of obsessive-compulsive disorder involve medications that work in conjuction with cognitive-behavioural
therapy, the most promising of which is D-cycloserine