ObjectiveGay and bisexual men are at an increased risk for eating disorders (EDs) and muscle dysmorphia (MD) compared with their heterosexual counterparts. Existing dissonance‐based (DB) EDs prevention programs for this population have been evaluated in the United States; however, these programs have not been evaluated in the Brazilian context. Thus, we investigated the feasibility, acceptability, and efficacy of a DB ED prevention program (i.e., the PRIDE Body Project) among Brazilian cisgender gay and bisexual men.MethodEligible men were randomly assigned to either a DB intervention (n = 74) condition or an assessment‐only control (AOC) condition (n = 75). Participants completed measures assessing ED and MD risk and protective factors at baseline, post‐intervention, 1‐month, 6‐month, and 1‐year follow‐up. Those in the intervention condition also completed acceptability measures.ResultsFeasibility and acceptability ratings were highly favorable. Regarding efficacy, post‐intervention results were not significant, except for self‐objectification, which showed a significantly greater decrease in the DB condition compared with the AOC condition at all time‐points of follow‐ups (Cohen's d = −0.31 to −0.76). At follow‐up, the DB condition showed significantly greater decreases in appearance‐ideal internalization, drive for muscularity, self‐objectification, ED and MD symptoms at 1‐month, 6‐month, and 1‐year follow‐ups (d = −0.33 to −0.92) compared with the AOC condition. Significant increases were observed in the DB compared with the AOC condition for body appreciation at 1‐month, 6‐month, and 1‐year follow‐ups (d = 0.31–0.81).DiscussionResults support the feasibility, acceptability, and efficacy of the PRIDE Body Project up to 1‐year in Brazilian cisgender gay and bisexual men.Trial RegistrationBrazilian Registry of Clinical Trials (ReBEC; available at http://www.ensaiosclinicos.gov.br/) number of registration: RBR‐62fctqz.