OBJECTIVE In this cohort study, we assessed the impact of smoke-free work-site policies on smoking cessation behaviors. METHODS Smokers were tracked as part of the Community Intervention Trial for Smoking Cessation. Telephone surveys were administered to 1967 employed smokers in 1993 and 2001. Data were gathered on personal and demographic characteristics, tobacco use behaviors, and restrictiveness of worksite smoking policies. RESULTS People who worked in environments that changed to or maintained smoke-free policies between 1993 and 2001 were 1.9 times more likely (odds ratio [OR] = 1.92; 95% confidence interval [CI] = 1.11, 3.32) than people whose worksites did not do so to have stopped smoking by 2001. Continuing smokers decreased their average daily consumption by 2.57 cigarettes. People working in environments that had smoke-free policies in place in both 1993 and 2001 were 2.3 times more likely (OR=2.29; 95% CI=1.08, 4.45) than people not working in such environments to have quit by 2001, and continuing smokers reported a decline in average daily consumption of 3.85 cigarettes. CONCLUSIONS Smoke-free worksite policies help employees reduce their cigarette consumption and stop smoking.