On the basis of data available from two representative samples of lung cancer deaths in the United States as well as national mortality statistics and other epidemiologic studies, the lung cancer mortality rate has risen substantially between 1914 and 1968 among persons who never smoked cigarettes. For white males the relative increase for ages 35--84 years has been about 15-fold; the relative increase for ages 65--84 years has been about 30-fold. For white females the relative increase for ages 35--84 years has been about sevenfold. Most of the relative increase occurred before 1935 and was probably due to changes in diagnostic criteria. However, increases have continued up to the present for male nonsmokers, who now apparently have an annual age-adjusted lung cancer death rate of about 25 per 100,000 persons between the ages 35--84 years. The rising lung cancer rate among nonsmokers indicates that factors in addition to personal cigarette smoking have had a significant effect on the mortality rate from this disease. In spite of the limited quality of these data, they suggest that a more complete understanding of lung cancer etiology is needed.