This paper reports on the evaluation of an Australian whole-of-community social marketing intervention targeted to adolescents, parents and community members over a period of two years. The intervention targeted social norms, aiming to reduce inflated perceptions of the prevalence of underage drinking and also increase the age at which alcohol initiation was considered acceptable. When compared with a control community, the intervention community saw an increase of 6 months in the average age at which it was perceived to be acceptable for young people to taste alcohol and 5 months in the average 'acceptable' age to have weak/watered down alcohol. There was also a reduction in the perception of the prevalence of alcohol consumption by young people to a level consistent with actual underage drinking rates. These results suggest that whole-of-community social marketing interventions may change perceptions of underage drinking which has the potential to reduce parental supply of alcohol and influence the social norms regarding alcohol consumption and thus reduce underage drinking.