Recent recommendations for increases in desirable body weights are based upon studies which did not consider the potential confounding effect of cigarette consumption on body weight. We investigated the relation between tobacco use and several anthropometric measurements in 12,103 men and women 19-74 years of age in the United States examined between 1976 and 1980 during the Second National Health and Nutrition Examination Survey (NHANES II). Cigarette smokers weighed less (mean +/- standard error = 69.8 +/- 0.2 kg) and were leaner (body mass index (weight (kg)/height (m)2) = 24.6 +/- 0.1) than nonsmokers (72.5 +/- 0.2 kg and 25.7 +/- 0.1, respectively), controlling for age and sex. Body leanness increased with the duration (but not intensity) of smoking. Ex-smokers were not heavier or fatter than nonsmokers, and these groups experienced similar weight gain after age 25 (approximately 6 kg in men, 9 kg in women), while current smokers gained substantially less weight (3.5 kg in men, 5.4 kg in women). Compared to nonsmokers, former and current smokers were also slightly taller. Most of these associations were evident in both sexes and all ages evaluated, and were not explained by differences in caloric intake, physical activity, illness, or socioeconomic status. Our findings suggest that the increased mortality observed among lean individuals in previous studies may have been due to smoking rather than leanness per se, and that as a result, currently accepted desirable body weights may be overestimated.