During epidemiologic investigations of vascular complications of diabetes in Warsaw the habit of cigarette smoking was analyzed in the subjects studied (4,530 diabetics). It was found that in the group of diabetics the number of ex-smokers was much greater (p < 0.01) and that of present smokers lower (p < 0.01) than in a representative sample of the Warsaw population. Furthermore, it was observed that in the subgroup of insulin-treated diabetics the number of smokers was highest and the number of ex-smokers and nonsmokers was lowest in relation to other treatment subgroups.