Five-year follow-up results for 8,278 men who in mail surveys had reported their cigarette smoking and dietary habits showed: (1) an index for vitamin A intake to be negatively associated with lung cancer incidence at all levels of cigarette smoking; (2) this association to be more clearly expressed in the subset of histologically proven pulmonary carcinomas other than adenocarcinoma; and (3) the positive association between cigarette smoking and lung cancer to obtain irrespective of the dietary level of vitamin A or related factors. The findings are in accordance with experimental results on animals and call for further exploration of the role of nutritional factors in the development of human lung cancer.