Body dysmorphic disorder is a distressing and often disabling condition characterised by a preoccupation with imagined or slight physical defects in appearance. It has been recognised as a mental disorder for many years (and named body dysmorphic disorder since 1980), but epidemiological studies and clinical trials have been few. To a large extent, the disorder has been ignored by the mental health community, who often fail to elicit the diagnosis. This article reviews the diagnostic criteria for the disorder, its validity and its relationship to other disorders such as obsessive-compulsive disorder, anorexia nervosa, social phobia and somatisation disorders. The course of the illness, its aetiology and treatment approaches are discussed. As research is growing alongside an increase in patient presentations, body dysmorphic disorder requires a coherent response from healthcare services.