Background Anxiety disorders are common, often start in childhood and run a chronic course. As such there is a need for effective prevention. Methods We conducted a systematic review and meta‐analyses of randomized, controlled trials to prevent the onset of anxiety disorders in ‘at risk’ young people. Diagnostic and symptom outcomes were examined. Putative moderators were tested as was publication bias. Results We included 16 trials (2545 young people). Two trials reported diagnostic outcomes, and significant effects were found for these at end‐of‐programme (RR = .09, 95%CI = .02 to .16), 6‐ (RR = .17, 95%CI = .06 to .27) and 12‐month (RR = .31, 95%CI .17 to .45) follow‐ups. Based on 16 trials, improved anxiety symptoms were significant compared to nonattention controls only, with small effect sizes reported by young people at the end‐of‐programmes, 6‐ and 12‐month follow‐ups; and by parents at the end of the programmes and 12‐, but not 6‐, month follow‐ups. There was no evidence of significant moderation or publication bias. Conclusions Fourteen studies included children and young people who presented with elevated anxiety symptoms, but anxiety disorder was not ruled out in the participants in these studies. Hence, these studies might be reporting results of mixed prevention/early intervention programmes. Prevention programmes that target developmental risk factors, not only disorder maintaining factors, appear most promising. The clinically meaningful impact of anxiety disorder prevention programmes remains unknown.