In this trial adolescent girls with body dissatisfaction (N=481; M age=17) were randomized to an eating disorder prevention program involving dissonance-inducing activities that reduce thin-ideal internalization, a prevention program promoting healthy weight management, an expressive writing control condition, or an assessment-only control condition. Dissonance participants showed significantly greater reductions in eating disorder risk factors and bulimic symptoms than healthy weight, expressive writing, and assessment-only participants and healthy weight participants showed significantly greater reductions in risk factors and symptoms than expressive writing and assessment-only participants from pretest to posttest. Although these effects faded over 6-month and 12-month follow-up, dissonance and healthy weight participants showed significantly lower binge eating and obesity onset and reduced service utilization through 12-month follow-up, suggesting both interventions have public health potential.