OBJECTIVES: To evaluate the impact of workplace smoking bans on cigarette consumption among continuing smokers over a two-year period. DESIGN: Two cross-sectional surveys and a longitudinal sample of smokers questioned about their smoking behaviour six months and two years after implementation of a workplace smoking ban. SUBJECTS: Workers in 46 government offices in Australia. The cross-sectional survey six months after the ban included 3388 workers, whereas the survey two years after the ban included 3982 workers. The longitudinal cohort study included 107 workers who were identified as current smokers in both surveys. MAIN OUTCOME MEASURES: Smokers were asked to report usual daily cigarette consumption on both workdays and leisure days one month before implementation of the ban, and six months, and two years afterwards. RESULTS: From six months to two years after the ban, the cross-sectional data showed an increase in cigarette consumption of 1.3 cigarettes per day. The longitudinal sample of smokers reported an increase in workday cigarette consumption of 1.7 cigarettes per day. A previous study of workers in the same worksites found a reduction in consumption of 5.2 cigarettes per day from before the ban to six months after. Over a two-year period we estimate that the net effect of the workplace smoking ban was to reduce cigarette consumption by about 3.5 cigarettes per day. CONCLUSIONS: Reductions in cigarette consumption among smokers frequently seen after implementation of a worksite smoking ban may diminish over time. This effect is more likely to occur when the initial response to a smoking ban is a large reduction in cigarette consumption.