An equation is presented which considers the number of smokers who would have developed cancer of the respective site in the absence of smoking. The value of f is an average value over the years relevant for the final deaths, typified by the figures for 1965 when 52% of males and 34% of females smoked. Some degree of uncertainty with regard to the exact value of the mortality ratio must remain unsolved. When this ratio is high, as in bronchogenic cancer, the difference in number of deaths attributed to smoking varies little with variation in m. Incidences for bronchogenic carcinoma are still rising. The American Cancer Society estimated that there will be 93,000 new cases in 1976. The present data indicate that 23.5% of all cancer deaths in 1974 were excess deaths due to cigarette smoking. A similar computation for 1974, restricted to males, indicated that 32.7% of all cancer deaths also represented excess deaths due to cigarette smoking. Whereas the data on lung cancer for 1975 are not yet complete, there was a 6% increase over 1974 in deaths from respiratory cancer. This large increase suggests that by 1975 at least 1/4 of all cancer deaths were unnecessarily caused by cigarette smoking.