This article reports on one of the few experimental studies in Europe to examine work site smoking cessation. The study examined whether a comprehensive intervention (self-help manuals, group courses, a mass media campaign, smoking policies, and a second-year program) is more effective than a minimal intervention (self-help manuals only). Eight work sites participated in the study. The effect of treatment on smoking cessation depended on nicotine dependency levels: Heavy smokers had more success with the comprehensive smoking cessation intervention than with the minimal intervention (with respect to both 14-month quit rate and 6-month prolonged abstinence). For heavy smokers, exposure to mass media exhibitions or to group courses had a beneficial effect on prolonged abstinence. Comprehensive programs may be most appropriate in Dutch work sites with large proportions of heavily addicted smokers.