Cross-sectional associations between smoking habits, body mass index, and waist-hip ratio (WHR) were examined in 1122 men aged 19 to 102 years. Weight and body mass index were significantly lower in cigarette smokers than in nonsmokers when age was taken into account. The WHR in smokers was significantly higher than in nonsmokers. A graded dose-response relationship was found between the number of cigarettes smoked and the WHR. Longitudinal associations between changes in smoking habits and changes in the WHR were examined during follow-up visits. In the period between these pairs of visits, weight increased when subjects quit smoking and decreased when they started smoking, as expected. The increase in WHR among those who quit smoking was, however, significantly less than the expected increase if smoking had continued. The WHR in those who started smoking actually increased despite their loss of weight. These paradoxical changes in WHR indicate that there are harmful effects of cigarette smoking on the pattern of distribution of body fat. These facts introduce still another reason to suggest that the decision to initiate or to continue smoking to control body weight is unwise.