The age-adjusted risk for lung cancer among over 120,000 male current cigarette smokers in the American Cancer Society's 1959-1972 prospective study was analyzed according to tar yield and quantity smoked per day. At each quantity level, the risk increased with increasing tar yield, and at each tar level, the risk increased with numbers of cigarettes smoked daily. The risks in smokers of cigarettes with the lowest yields, however, far exceeded those of former smokers and nonsmokers. The excess lung cancer risk for current smokers was directly proportional to the estimated total milligrams of tar consumed daily: SMR = 100 + 1.731 x milligrams tar per day. Tar yields today are much lower than they were at the time of this study and presage an eventual reduction (but not elimination) of lung cancer risk for those who continue to smoke cigarettes, especially among lifetime smokers of low-tar cigarettes.