Objective: Interpersonal psychotherapy (IPT) prevents weight gain in adults with obesity and binge-eating-disorder, and is especially effective among those with increased psychosocial problems. However, IPT was not superior to health education (HE) to prevent excess weight gain at 1-year follow-up in 113 adolescent girls at high-risk for excess weight gain because of loss-of-control eating and high body mass index (BMI; kg/m2; Tanofsky-Kraff et al., 2014). Method: Participants from the original trial were recontacted 3 years later for assessment. At baseline, adolescent- and parent-reported social-adjustment problems and trait anxiety were evaluated. At baseline and follow-ups, BMIz and adiposity by dual-energy x-ray absorptiometry were obtained. Results: Nearly 60% were reassessed at 3 years, with no group differences in participation (ps ≥ .70). Consistent with 1 year, there was no main effect of group on change in BMIz/adiposity (ps ≥ .18). In exploratory analyses, baseline social-adjustment problems and trait-anxiety moderated outcome (ps < .01). Among girls with high self-reported baseline social-adjustment problems or anxiety, IPT, compared to HE, was associated with the steepest declines in BMIz (p < .001). For adiposity, girls with high or low anxiety in HE and girls with low anxiety in IPT experienced gains (ps ≤ .03), while girls in IPT with high anxiety stabilized. Parent-reports yielded complementary findings. Conclusion: In obesity-prone adolescent girls, IPT was not superior to HE in preventing excess weight gain at 3 years. Consistent with theory, exploratory analyses suggested that IPT was associated with improvements in BMIz over 3 years among youth with high social-adjustment problems or trait anxiety. Future studies should test the efficacy of IPT for obesity prevention among at-risk girls with social-adjustment problems and/or anxiety.