Background: Long-term maintenance of weight loss remains a therapeutic challenge in obesity treatment. Objective: This multicenter, double-blind, placebo-controlled study was designed to test the hypothesis that orlistat, a gastrointestinal lipase inhibitor, is significantly more effective than a placebo in preventing weight regain Design: Obese subjects who lost ≥8% of their initial body weight during a 6-mo lead-in of a prescribed hypoenergetic diet (4180-kJ/d deficit) with no adjunctive pharmacotherapy were randomly assigned to receive placebo, 30 mg orlistat, 60 mg orlistat, or 120 mg orlistat 3 times daily for 1 y in combination with a maintenance diet to help prevent weight regain. Of 1313 recruited subjects [body mass index (in kg/m2): 28-43], 729 subjects lost ≥8% of their initial body weight during the 6-mo weight-loss lead-in period and were enrolled in the double-blind phase. Results: After 1 y, subjects treated with 120 mg orlistat 3 times daily regained less weight than did placebo-treated subjects (32.8 ± 4.5% compared with 58.7 ± 5.8% regain of lost weight; P < 0.001). Moreover, more subjects in the 120-mg orlistat group than in the placebo group regained ≤25% of lost weight (47.5% of subjects compared with 29.9%). In addition, orlistat treatment (120 mg 3 times daily) was associated with significantly greater reductions in total and LDL-cholesterol concentrations than was placebo (P < 0.001). Conclusion: The use of orlistat during periods of attempted weight maintenance minimizes weight readjustment and facilitates long-term improvement in obesity-related disease risk factors.