OBJECTIVE: To examine the impact of workplace smoking bans on smoking behavior of employees. PARTICIPANTS: A total of 1469 current or former smokers (intervention group) employed in smoke-free hospitals and 920 current or former smokers (comparison group) employed in non-smoke-free workplaces were surveyed to determine smoking behavior. DESIGN: This cross-sectional study is part of a larger, ongoing prospective study. The study design was quasi-experimental. We randomly selected sites consisting of a hospital and a corresponding community. Furthermore, we randomly selected subjects from hospitals and their corresponding communities. MAIN OUTCOME MEASURES: Postban quit ratio and progression along the stages-of-change continuum. METHODS: The Cox proportional hazards model was used to compare the postban quit ratio between the intervention and comparison groups. The Cochran-Mantel-Haenszel analysis of variance statistic was used to compare groups on the stages-of-change variables. RESULTS: Beginning with the smoking ban and continuing for 5 years after implementation, statistically significant differences in the postban quit ratio were observed between employees of smoke-free hospitals who were smokers and counterparts in the community (P<.001). Despite preban differences in smoking intensity, the overall difference in postban quit ratios remained significant even after multivariate adjustment for socioeconomic, demographic, and smoking intensity variables. For those sites that were 5 years postban, the quit ratio was 0.506 in smoke-free workplaces compared with 0.377 in workplaces where smoking was permitted. In all but 1 category, the intervention group was further along the stages-of-change continuum toward quitting smoking than the comparison group (P<.001). CONCLUSION: American hospitals' experiences with smoking bans, which directly affect more than 5 million workers, should be examined by other industries as a method of improving employee health. Workplace smoking bans could also be effective in saving lives, reducing health care costs, addressing safety concerns, and decreasing operating and maintenance expenses of employers.