Maintenance of weight loss continues to be a critical concern in behavioral treatment programs. Problems with the acquisition and/or application of behavioral skills are a likely contributor to relapse. However, biological models, especially the hypothesis of a body weight setpoint, are being offered increasingly as alternative explanations for maintenance failure. Within the context of these sometimes opposing viewpoints the present study describes long-term weight outcomes for 114 men and 38 women assessed annually for 4 or 5 years following completion of a 15 week behavioral weight loss program. Although significant mean weight loss was evident at long-term follow-up, a negatively accelerating pattern of weight regain was the predominant outcome. Less than 3 percent of the subjects were at or below their posttreatment weight on all follow-up visits. Consistent sex differences were found, with women having better weight loss maintenance than men. Implications and potential future directions are discussed.