The purpose of this study was to determine prospectively the safety and efficacy of an adjustable silicone gastric band and reservoir system for the treatment of morbid obesity. Between 1992 and 1995, forty primary procedures were performed. Twenty-six females and 14 males entered the study. The mean age of the subjects was 34 years (range 19 to 51 years). Mean body mass index was 50 kg/m2 (range 39 to 75 kg/m2). There were no deaths. Mean body mass index (in kg/m2) at follow-up visits was 38.4 at 1 year, 38.0 at 2 years, 40.2 at 3 years, and 40.4 at 4 years. These decreases were significant at P <0. 001. Thirty-two reoperations (12 intra-abdominal procedures and 20 abdominal wall procedures) have been necessary to maintain efficacy or correct complications. At the four-year interval, the reoperation rate of 80% was unsatisfactory. The excess weight loss has been 41% for those subjects who have an intact gastric band system and continue in the study. Improvements to the implantable band and/or operative technique must be implemented and studied long term if this procedure is to become an accepted surgical treatment for severe obesity.