To examine the diagnostic stability and outcome of hypochondriasis, the authors followed 50 patients with this disorder and 50 age- and sex-matched control subjects after 1 year. After 1 year, two-thirds of the subjects continued to meet criteria for hypochondriasis, and the remaining third had persisting hypochondriacal symptoms. The hypochondriacal subjects were improved on most measures but still differed from the control subjects with regard to attitudes, perceptions, and behaviors that had distinguished them initially. More severe symptoms, longer duration of illness, and coexisting psychiatric illness were predictive of a worse outcome. The data indicate that the diagnosis of hypochondriasis is stable over time, and that, although symptoms wax and wane, characteristic features persist. The findings underscore the importance of diagnosing and treating hypochondriasis in medical outpatients.