A proportional mortality study of 1,075 iron ore miners in Lorraine, France, who died between 1960 and 1976 showed a significant excess of lung cancer mortality (proportionate mortality ratio = 2.25). Moreover, proportionate lung cancer mortality increased with the duration of work underground (proportionate mortality ratio = 4.24 for subjects who worked underground for more than 30 years) and was higher among pneumoconiotic (siderotic) miners (proportionate mortality ratio = 3.85) than among nonpneumoconiotic miners. These results were confirmed by a case-control study nested in the mortality study. Smoking habits could not be estimated retrospectively with sufficient accuracy to be taken into account. Although the proportion of smokers among contemporary iron ore miners is larger than in the French male population, occupational factors may also play a role; radiation exposure can be ruled out because there is no detectable radioactivity in the Lorraine mines, but dust exposure may be considered as an etiologic factor owing to the relationship between siderosis and lung cancer.