© 2018 Background: Lithium and quetiapine can cause weight gain, but their comparative longer term anthropometric effects are unknown, as are the potential moderating effects of baseline binge-eating (BE) behavior. Methods: We assessed 6 month changes in body weight, body mass index (BMI) and waist circumference in 482 adults with DSM-IV bipolar disorders who participated in a comparative effectiveness study of lithium and quetiapine with evidence-based adjunctive treatment (Bipolar CHOICE). Anthropometric measurements were obtained at baseline, and at 2, 4, 6, 8, 12, 16, 20, and 24 weeks. BE behavior was defined as affirmative responses to MINI items M1 and M3 at baseline. Data were analyzed using a mixed model repeated measures approach, adjusted for baseline values of dependent measures. Results: On average, body weight and BMI increased over 6 months with lithium and quetiapine. However, those treated with quetiapine experienced greater increases from baseline in body weight (peak change, + 3.6 lbs. vs. + 1.4 lbs.) and BMI (peak change, + 0.6 kg/m2 vs. + 0.3 kg/m2), starting at 2 weeks (group x time, F8,3052= 2.9, p = 0.003 for body weight, F8,3052= 3.0, p = 0.002 for BMI). Significant increases in waist circumference were observed only with quetiapine. The relationship between drug treatment and changes in body weight (group x time x binge eating status, F1,2770= 2.0, p = 0.002), BMI (F1,2767= 2.0, p = 0.002), and waist circumference (women only, F25,1621= 2.9, p < 0.0001) were moderated by BE behavior. The largest increases over 24 weeks in body weight and BMI, and waist circumference in women, occurred for quetiapine-treated patients with baseline binge-eating, relative to quetiapine-treated patients without binge eating and lithium-treated patients with or without baseline binge-eating. Limitations: Bipolar CHOICE was not designed to study anthropometric outcomes. Conclusions: Greater changes in body weight, BMI, and waist circumference occurred with quetiapine- versus lithium-based treatment over 6 months of treatment. The effects of study drugs on these anthropometric measures were moderated by BE behavior at baseline.