['This study examined effects of a behavioral weight management intervention on body image (evaluative and investment dimensions) and explored the potential mediating role of structured and lifestyle physical activity (PA).', 'The study was a longitudinal randomized controlled trial, including a 1-yr behavior change intervention and a 2-yr follow-up (225 women, 37.6 ± 7 yr, body mass index = 31.5 ± 4.1 kg·m). Statistical analyses comprised mixed-design ANOVAs with repeated measures, bivariate/partial correlations, and mediation analyses.', 'Body image improved considerably in both groups, favoring the intervention group (small to moderate effect sizes: 0.03-0.05), but began to deteriorate from 12 to 24 months, especially in the intervention group. Consequently, at 24 months, between-group differences were small and did not reach significance. Yet, levels of body dissatisfaction and dysfunctional investment remained below initial values (for both groups). Results were similar for both body image dimensions. Structured PA (at 12 and 24 months) and lifestyle PA (at 24 months) were positively associated with (r > -0.25, P < 0.05) and partially mediated body image improvements, especially in the investment component (95% confidence interval of -1.88 to -0.27 for structured PA at 12 months, 95% confidence interval of -1.94 to -0.21 for lifestyle PA at 24 months). In general, change in evaluative body image was not mediated by exercise participation, seeming more dependent on weight change.'] Does physical activity predict changes in body image during obesity treatment in women?