Although hypochondriasis has been one of the most durable disease concepts in psychopathology, little is known about its epidemiology and treatment. In this article, we review the last three decades of research into these two aspects of hypochondriasis. According to DSM-IV, hypochondriasis is a distressing preoccupation with the fear or thought, based on physical sensations, that one has a serious disease. The prevalence of hypochondriasis in the general population is unknown; however, studies in primary care suggest that the prevalence in this setting is between 0.8 and 4.5%. There are, at present, no conclusive data about specific risk factors for hypochondriasis, although patients with hypochondriasis have higher rates of anxiety, depressive and other somatoform disorders than patients without the disorder. To date, there have been no studies documenting a genetic or familial predisposition for hypochondriasis, or for somatoform disorders in general. Cognitive behavioural therapy has been shown in controlled studies to be efficacious in the treatment of hypochondriasis. Although the evidence is stronger for individual therapy, group cognitive-behavioural therapy may also be useful. Other therapies such as supportive or psychoanalytical psychotherapy may be efficacious for certain patients, but the lack of standardised treatments and controlled studies makes them a less preferable treatment option at present. Little is known about the pharmacological treatment of primary hypochondriasis. The limited number of published studies and the absence of controlled trials make it impossible to be certain of the efficacy of existing medications. On the basis of the available information, however, it appears that the selective serotonin reuptake inhibitors hold promise for the treatment of this disorder. However, more information is needed for their efficacy to be clearly established.