To test the eating disorder expectancy theory contention that expectancies for reinforcement from thinness play a causal role in body dissatisfaction and eating disorder symptoms, the authors manipulated expectancies in 2 studies. Participants were exposed to either a psychoeducational intervention or an experimental manipulation of thinness and restricting expectancies. Study 1 participants were symptomatic college women who attended 3 experimental sessions and 1 follow-up session, each 1 week apart. Study 2 participants were high school girls who received the 3 experimental sessions clustered into 2 meetings; they completed symptom measures at baseline and at follow-up. In both samples, the thinness expectancy manipulation produced greater declines in thinness expectancies and body dissatisfaction than did the psychoeducational intervention. For high school girls, the thinness expectancy manipulation also produced a greater decline in overall eating-disordered attitudes. These results provide further support for the role of expectancies in the etiology of eating-disordered behaviors.