A study of 922 college men was made relating their morphological characteristics as students to their subsequent histories of smoking 13 yr after graduation, in order to ascertain the extent to which the different classes of nonsmokers, cigarette smokers, pipe smokers, and cigar smokers were phenotypically and genotypically conditioned. Significant differences in physique were found between smokers and nonsmokers and in accordance with the form of smoking adopted. Smokers were consistently greater than nonsmokers in height and weight and in the dimensions of the head, face, shoulders, chest, hip, leg, and hand. The findings delineate constitutional differences between smokers and nonsmokers and among the several varieties of smokers. Smoking behavior thus appears to be in part a reflection of the biological or genetic make-up of the individual.