Background: While clean indoor air (CIA) policies are intended to reduce exposure to second-hand smoke in the workplace, restrictions in public workplaces have the potential to discourage youth smoking. There is growing evidence from cross-sectional and ecological studies, but limited evidence from longitudinal studies that this is so. Objective: To evaluate the association between local CIA policies and smoking behaviours among Minnesota youth over time. Design, setting and subjects: A cohort of 4233 Minnesota youths, ages 11 to 16 at baseline, was interviewed via telephone for 6 years (2000-2006). Individual, family and community level variables were collected from participants every 6 months. A generalised estimating equation (GEE) logistic regression was used to assess the relationship between CIA policies and past-month smoking in youth over time. The analysis was controlled for potential confounders at individual and community levels. Results: There was not significant association between CIA policies and youth smoking behaviours in the multivariate analyses. At the individual level, parental smoking significantly increased the odds of smoking nearly 40% and close friend smoking increased the odds of past-month smoking by nearly 100% for each close friend. Banning smoking in the home was significantly associated with a 12% reduction in the odds of past-month smoking. Conclusion: After accounting for other community and individual level factors known to be associated with youth smoking, there was no significant association between CIA policies and past-month smoking for youth over time.