BACKGROUND: Alcohol policies around the world seek to delay the initiation of drinking. This is partly based on the influential idea that earlier initiation is likely to cause adult alcohol problems. This study synthesises robust evidence for this proposition. METHODS: Systematic review of prospective cohort studies in which adolescent measurement of age of first drink in general population studies was separated by at least 3 years from adult alcohol outcomes. EMBASE, Medline, PsychINFO and Social Policy and Practice were searched for eligible studies, alongside standard non-database data collection activities. Data were extracted on included study methods and findings. Risk of bias and confounding was assessed for individual studies and a narrative synthesis of findings was performed. RESULTS: The main finding was the meagre evidence base available. Only five studies were eligible for inclusion in this review. The existence of effects of age of first drink on adult drinking and related problems were supported, but not at all strongly, in some included studies, and not in others. Rigorous control for confounding markedly attenuates or eliminates any observed effects. CONCLUSIONS: There is no strong evidence that starting drinking earlier leads to adult alcohol problems and more research is needed to address this important question. Policy makers should, therefore, reconsider the justification for delaying initiation as a strategy to address levels of adult alcohol problems in the general population, while also addressing the serious acute harms produced by early drinking.