Statistical data on smoking and dietary habits in northern and southern Italy were compared and related to mortality rates for lung cancer. Age-adjusted mortality rates for lung cancer in the years 1980 and 1982 were lower in southern than in northern Italy. The proportion of smokers, as surveyed in 1977, was similar in the two geographical areas. Dietary habits in southern Italy, however, were characterized during the years 1960 through 1965, by a low consumption of saturated and polyunsaturated lipids, and a high consumption of foods of vegetable origin. Our data suggest that diet may modify the carcinogenic effect of tobacco in lung cancer.