- Smoking is the most important preventable cause of chronic disease in the western world. Many smokers want to quit, but have difficulty overcoming the addictive effect of nicotine. To assess the quitting rate of smokers who participated in smoking cessation groups and to characterize predictors of success or failure over a 1-3 years follow-up period. We studied 89 participants in 7 groups. Questionnaires were completed at baseline and after a follow-up period of 1 to 3 years. Smoking cessation was determined by self-report and a carbon monoxide breath test. Of the 89 participants in the support groups 76 (85%) were located. An intention-to-treat analysis was done for these participants. At follow-up 25 (33%) were non-smokers. There was a 95% agreement rate between self-report of smoking status and CO breath analysis. There were no differences between quitters and non-quitters in education level, gender, age at initiation of smoking, previous quit attempts, extent of participation in group meetings, concern about gaining weight, Fagerstrom index, or the number of close friends or relatives who smoke. Belief in one's ability to quit, satisfaction with group meetings, and spouse support were significantly associated with success (P < 0.01). The quit rate was 33%. Self-report is a reliable method for assessing smoking status. Smokers' belief in their ability to quit must be reinforced. Spouse participation in some group meetings may be beneficial, as may the involvement of a dietician and an expert on exercise. Follow-up "booster" meetings may also help.