Background: Although hypochondriasis is generally thought to be a chronic and stable condition with a relatively low remission rate, this disorder remains understudied. Methods: This is a 4- to 5-year prospective case-control study of DSM-III-R hypochondriasis. Medical outpatients meeting DSM diagnostic criteria for hypochondriasis completed an extensive research battery assessing hypochondriacal symptoms, medical and psychiatric co morbidity, functional status and role impairment, and medical care. A comparison group of nonhypochondriacal patients from the same setting underwent the same battery. Four to 5 years later, both cohorts were, re interviewed. Results: One hundred twenty hypochondriacal and 133 nonhypochondriacal comparison patients were originally studied. Follow-up was obtained on 73.5% (n = :186) of all patients. At follow-up, the hypochondriacal sample was significantly (P<.001) less hypochondriacal and had less somatization (P<.001) and disability than at inception, but 63.5% (n=54) still met DSM-III-R diagnostic criterial. When compared with the comparison group using repeated measures multivariate analysis of variance, these changes remained statistically significant (P<.0001). Changes in medical and psychiatric comorbidity did not differ between the 2 groups. When hypochondriacal patients who did and did not meet diagnostic criteria at follow-up were compared; the latter had significantly less disease conviction (P<.05) and somatization (P<.01) at inception, and their incidence of major medical illness during the follow-up period was significantly (P<.05) greater. Conclusions: Hypochondriacal patients show a considerable decline in symptoms and improvement in role functioning over 4 to 5 years but two thirds of them still meet diagnostic criteria. Hypochondriasis, therefore, carries a very substantial, long-term burden of morbidity, functional impairment, and personal distress.