Lung cancer is the most common malignancy in the United States and is ranked second only to bladder cancer in the proportion of cases thought to be due to occupational exposures. We review the epidemiology of occupational lung cancer, focusing on agents identified as pulmonary carcinogens by the International Agency for Research on Cancer. We derive estimates of overall relative risks from the major studies of these lung carcinogens, and we also provide estimates of the number of exposed workers. Using our data as well as estimates from other authors, we estimate that approximately 9,000-10,000 men and 900-1,900 women develop lung cancer annually in the United States due to past exposure to occupational carcinogens. More than half of these lung cancers are due to asbestos. This estimate is likely conservative, in that we have restricted our analysis to confirmed lung carcinogens and have ignored occupations with documented excess risk but for which the specific agents are unknown. Also, our estimate of the proportion of workers exposed in the past is probably too low. Our estimate should be viewed only as broad approximation. Nevertheless, it is in line with other estimates by authors using different methods. The current number of cases estimated to be due to occupational exposure reflects past high exposures and is likely to drop in the future, unless other occupational lung carcinogens are confirmed or new carcinogens are introduced into the workplace.