Body dysmorphic disorder (BDD) is defined as a preoccupation with an imagined or minimal defect in appearance. Virtually any body part can be the focus of concern, although preoccupations with the hair, nose and skin are particularly common. Associated features include repetitive and often ritualistic behaviours, such as mirror checking and requests for reassurance, as well as ideas or delusions of reference. The degree of impairment associated with the disorder is variable, but most patients experience significant functional impairment as a result of their concerns.While this often secret disorder has been described for more than a century and reported around the world, it has received little empirical investigation. Nonetheless, emerging data suggest that BDD is frequently a chronic disorder that usually begins during adolescence. Psychiatric hospitalisation and suicide attempts are common in patients with BDD. Disorders that are frequently comorbid include major depression, social phobia and obsessive-compulsive disorder. The prevalence of BDD among patients with other psychiatric disorders, such as atypical depression, obsessive-compulsive disorder and social phobia, appears to be relatively high.The majority of patients with BDD seek often costly nonpsychiatric therapies, such as surgical or dermatological interventions. These approaches are usually unsuccessful. In contrast, preliminary data from noncomparative studies suggest that serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors are often, and perhaps preferentially, effective in the treatment of BDD. Other preliminary data suggest that cognitive-behavioural strategies may also be useful. There are virtually no data on treatment-resistant BDD, but certain pharmacological approaches including augmentation, combination and switching strategies are sometimes effective.Further investigation of all aspects of this understudied disorder is greatly needed. Aspects that require particular attention are the epidemiology, clinical features, relationship to other psychiatric disorders, biology and, ultimately, aetiology and treatment response.