During the first 18 years of the Framingham Study there was a substantial decrease (39 per cent ) in the number of men smoking cigarettes and a moderate decrease (22 per cent) in the number of women smoking cigarettes. Except for a greater tendency of diabetic patients to quit smoking, there were no significant differences at baseline between smokers who quit and smokers who continued smoking. After quitting there was a short-term rise in weight for men. This rise led only to trivial changes in blood pressure and serum cholesterol levels. There was a beneficial impact on long-term vital capacity trends from quitting smoking.