BACKGROUND: The field of "medical outcomes" emphasizes effects of medical treatments on quality of life as seen from the patient's perspective. The increasing incidence of obesity has had tremendous impact on the physical, psychological, social, and economic health of our nation with important longterm implications for the development of future social and health care policies. This study evaluated the effects of clinically severe obesity on overall health status measured in a standardized fashion and the impact of durable weight loss achieved through surgical intervention. STUDY DESIGN: Patients scheduled for Roux-en-Y gastric bypass for treatment of obesity were prospectively evaluated. At the preoperative visit, each patient completed Short Form 36 (SF-36). Postoperatively, patients were again asked to complete SF-36, in person or through a telephone interview at an interim point (3 to 12 months) and after their weight had reached a plateau (>18 months). RESULTS: The mean body mass index (BMI) was 51+/-10 kg/m2 preoperatively (range 38 to 85 kg/m2). Mean BMI was 45+/-10 kg/m2 (range 33 to 78 kg/m2) at the interim point and 35+/-8 kg/m2 (range 28 to 55 kg/m2) at plateau. The weight change for the group was from 306+/-8 lb (138+/-4 kg) preoperatively to 211+/-55 lb (96+/-25 kg) at the plateau, with the average percent of excess body weight lost being 63+/-23% at the plateau. Preoperatively, patients with clinically severe obesity scored significantly lower than the normal population in all areas except Role Activities (Emotional Factors). At the plateau period, patients demonstrated significant improvement in limitations in all areas compared with preoperative values and scores were the same as (Physical Activities, Role Activities [Physical Factors], General Mental Health, General Health Perceptions), or significantly better than (Social Functioning, Role Activities [Emotional Factors], Bodily Pain, Vitality), the national "normal" population. CONCLUSION: Clinically severe obesity is a chronic disabling disease that results in significantly decreased health status in seven of the eight areas measured by SF-36. This disability resolves with successful weight reduction. In some areas, function even surpasses the national "normal" population. Surgical treatment of clinically severe obesity has a profoundly positive impact on patients' perception of their health status.