In this trial, adolescent girls with body dissatisfaction (N = 481, M age = 17 years) 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-ups, dissonance and healthy weight participants showed significantly lower binge eating and obesity onset and reduced service utilization through 12-month follow-up, suggesting that both interventions have public health potential.