["Journal of Child Psychology and Psychiatry, EarlyView. ", "\n\nBackground\nOmega‐3, a long‐chain fatty acid critical for brain structure and function, has been argued to be effective in reducing antisocial behavior, but findings are variable. This meta‐analysis examines 25 randomized controlled trials (RCTs) with a total of 2,889 participants.\n\n\nMethods\nThis study was registered with PROSPERO (CRD42021256959). Two separate analyses were conducted where the unit of analysis was independent studies and independent laboratories.\n\n\nResults\nSignificant effect sizes (p < .001) were observed for both analyses (g = .13, .14 respectively) and in the direction of omega‐3 supplementation reducing antisocial behavior. There was equivocal evidence of publication bias. Study quality was good. Stratified analyses were nonsignificant for age, gender, dose, sample size, and study quality, although the effect size was larger for unmedicated participants. Combining these data with a recent meta‐analysis on aggressive behavior produced an overall effect size of g = .22 for externalizing behavior based on 36 nonoverlapping RCTs.\n\n\nConclusions\nGiven that omega‐3 supplementation is relatively cheap, easy to implement, transfers well from the research environment to community settings, and has additional health benefits, it is suggested that it may be considered as an adjunctive intervention for the treatment of antisocial and externalizing behavior.\n\n"]