This paper discusses the methodologic issues one confronts when studying the impact of worksite smoking policies, using one such study as an example. Topics covered include defining the research questions, deciding on timing of measurements in relation to policy implementation, advantages and disadvantages of cohort versus cross-sectional research designs, and alternative measurement techniques. The sample study examined changes over one year in the smoking-related behaviors and attitudes of employees of a hospital that initiated a restrictive smoking policy, in relation to employees of a comparable hospital without a restrictive policy. The short term impact on ambient carbon monoxide was also examined. A case is made for studying the impact of smoking policy in the context of other strategies for reducing smoking prevalence at the worksite, such as individual treatment and organizational initiatives to motivate smoking cessation.