OBJECTIVES: This study tested the hypothesis that adoption and implementation of local policies regarding youth access to tobacco can affect adolescent smoking. METHODS: A randomized community trial was conducted in 14 Minnesota communities. Seven intervention communities participated in a 32-month community-organizing effort to mobilize citizens and activate the community. The goal was to change ordinances, merchant policies and practices, and enforcement practices to reduce youth access to tobacco. Outcome measures were derived from surveys of students before and after the intervention and from tobacco purchase attempts in all retail outlets in the communities. Data analyses used mixed-model regression to account for the clustering within communities and to adjust for covariates. RESULTS: Each intervention community passed a comprehensive youth access ordinance. Intervention communities showed less pronounced increases in adolescent daily smoking relative to control communities. Tobacco purchase success declined somewhat more in intervention than control communities during the study period, but this difference was not statistically significant. CONCLUSIONS: This study provides compelling evidence that policies designed to reduce youth access to tobacco can have a significant effect on adolescent smoking rates.