Meta-analysis was used to cumulate the results from 633 studies of smoking cessation, involving 71,806 subjects, that reported the proportion of successful quits. Self-care methods do not appear to be as effective as formal intervention methods. Instructional programs involving physicians were not more effective than other instructional programs. Conditioning-based techniques such as aversive methods had success rates similar to those of instructional methods, and among the instructional methods, those incorporating social norms and values were more successful than those relying solely on didactic approaches. Cumulation of quit rates from all available control groups indicated that, on average, 6.4% of the smokers could be expected to quit smoking without any intervention. This figure must be subtracted from the raw success rate to obtain the net success rate for each program. Directions for future research are discussed.