Commercial weight loss programs such as Weight Watchers (WW) offer widely recognized and accessible treatment, but typically produce weight losses that are modest relative to professionally delivered programs. This study tested the hypothesis that a novel weight loss approach that combined the fundamental components of professionally delivered behavioral weight loss (BWL) treatment with the existing WW program would produce better weight losses than WW alone; no differences were expected between the novel treatment and BWL alone. Participants were 141 overweight and obese adults (90% women, 67% non-White, mean age = 49.7 ± 9.2 years, mean BMI = 36.2 ± 5.5 kg/m2) randomly assigned to 48 weeks of BWL, 48 weeks of WW, or 12 weeks of BWL followed by 36 weeks of WW (Combined Treatment, CT). Assessments were conducted at baseline and weeks 12, 24, and 48, with weight change as the primary outcome. Linear mixed model analysis showed that 24-week weight losses did not differ significantly between treatment groups; however, weight losses at 48 weeks were greater in the WW group (M=6.0 kg, SE=0.8) compared to the CT group (M=3.6 kg, SE=0.8; p=0.032), with BWL not significantly different from either (M=5.4 kg, SE=0.8). Further, a greater proportion of WW participants lost 10% of baseline weight by 48 weeks compared to BWL or CT (36.7%, 13.0%, and 15.2%, respectively, p’s<0.05). This study shows that the WW program can produce clinically meaningful weight losses and provides no evidence that adding brief BWL to the WW program improves outcome.