To determine the benefits of social support for weight loss and maintenance, this study recruited participants (N = 166) either alone or with 3 friends or family members and then randomly assigned them to a standard behavioral treatment (SBT) or SBT with social support strategies. Participants recruited with friends had greater weight losses at the end of the 4-month treatment and at Month 10 follow-up. Both recruitment strategy and the social support manipulation affected treatment completion and weight- loss maintenance. In those recruited alone and given SBT, 76% completed treatment and 24% maintained their weight loss in full from Months 4 to 10. Among those recruited with friends and given SBT plus social support, 95% completed treatment and 66% maintained their weight loss in full.