Despite their growing popularity, worksite health-promotion programs have generally been characterized as having low participation rates, high attrition rates, and modest outcomes. This investigation identified the predictors of participation, attrition, and outcome of worksite smoking-cessation program. Subjects were regular cigarette smokers recruited from two worksites. Of 66 eligible smokers in the two worksites, 44 (67%) agreed to participate in the program. Fifty-five percent (24 of 44) of these completed the program. Of those completing the program, 29% had quit smoking by posttest and 17% were abstinent at the 6-month follow-up. Results indicated that a different set of variables predicted participation, attrition, and outcome. The significant predictors of smokers who participated were the length of cessation in previous abstinence attempts, the number of years they smoked, and the belief regarding personal vulnerability in contracting a smoking-related disease. Levels of pretest carbon monoxide along with attitudes regarding the adoption of smoking restrictions in the worksite predicted attrition. Posttest cessation was related to nicotine levels of cigarette brand smoked at pretest and pretest beliefs regarding postcessation weight gain. Abstinence at the 6-month follow-up was predicted by the number of co-workers who smoked and pretest concerns related to postcessation weight gain. The results are discussed in terms of future evaluation and intervention efforts.