Introduction and Aims: Mass media education campaigns targeting parents may influence parent factors that reduce adolescent drinking; however few such campaigns have been evaluated. Design and Methods: The Parents, Young People and Alcohol campaign included two phases of mass media advertising, Cogs and I See, to deliver consistent messages across multiple media channels. The campaign targeted Western Australian parents of 12–17 year olds with messages describing alcohol's effect on the developing brain and adolescent physical and mental health. The campaign reinforced the National Health and Medical Research Council (NHMRC) Guideline that for under 18s, not drinking is the safest option. Parent knowledge, attitudes and behaviours were assessed via cross-sectional surveys administered before the campaign (Time 1) and at two post-tests (Time 2; Time 3). Post-test campaign awareness and perceptions were also assessed. Results: Campaign awareness was high (48% Time 2; 80% Time 3) and over 86% of parents found the campaign believable and relevant at both post-tests. Increased knowledge of the NHMRC guideline and lower belief in alcohol myths were found at both post-tests compared to Time 1. Less positive attitudes to parental supply were found at Time 2, but were not sustained at Time 3. Parents were more likely to have discussed alcohol risks and limiting drinking with their child at Time 3, but parent-to-child alcohol supply did not change significantly. Discussion and Conclusions: The campaign achieved high awareness and positively influenced parental outcomes. Longer term campaign implementation supported by policy and environmental measures may be required to change parental supply.