Patients undergoing bariatric surgery lose substantial weight (> or = 50% excess weight loss [EWL]), but an estimated 20 per cent fail to achieve this goal. Our objective was to identify behavioral predictors of weight loss after laparoscopic Roux-en-Y gastric bypass. We retrospectively surveyed 148 patients using validated instruments for factors predictive of weight loss. Success was defined as > or =50 per cent EWL and failure as <50 per cent EWL. Mean follow-up after laparoscopic Roux-en-Y gastric bypass was 40.1 +/- 15.3 months, with 52.7 per cent of patients achieving successful weight loss. After controlling for age, gender, and preoperative body mass index, predictors of successful weight loss included surgeon follow-up (odds ratio [OR] 8.2, P < 0.01), attendance of postoperative support groups (OR 3.7, P = 0.02), physical activity (OR 3.5, P < 0.01), single or divorced marital status (OR 3.2, P = 0.03), self-esteem (OR 0.3, P = 0.02), and binge eating (OR 0.9, P < 0.01). These factors should be addressed in prospective studies of weight loss after bariatric surgery, as they may identify patients at risk for weight loss failure who may benefit from early tailored interventions.