This review examines whether reduction in smoking among smokers not currently interested in quitting (a) undermines or promotes future smoking cessation or (b) decreases the risks of developing smoking-related diseases. Systematic computer searches and other methods located 19 studies examining reduction and subsequent cessation and 10 studies examining reduction and disease risk. Because of the heterogeneity of methods and results, a meta-analysis could not be undertaken. None of 19 studies found that reduction undermined future cessation, and 16 found that reduction was associated with greater future cessation, including the two randomized trials of reduction versus nonreduction. The 10 trials of disease risk found conflicting results, and none was an adequate test. We conclude that (a) smoking reduction increases the probability of future cessation and (b) whether smoking reduction decreases the risks of smoking-related diseases has not been adequately tested.