An epidemiologic study of health hazards associated with uranium (7440611) milling was performed. Personnel records of 2,002 males from seven uranium mills were selected for inclusion in a retrospective cohort. Cohort members worked at least 1 year in uranium milling and did not work in uranium mining. Risk of mortality within the cohort was analyzed from 1940 to 1977 using the modified life table system. Observed deaths among the cohort were compared with number of deaths expected based on US death rates specific for cause, age, race, sex, and calendar period. Results were reported as the Standardized Mortality Ratio (SMR). Mortality due to many causes, including stroke, cardiovascular disease, alcoholism, cirrhosis, and all malignant neoplasms, was well below that expected. No statistically significant excesses of any malignancies were observed. A hypothesis of excess risk of lung cancer was not supported. An SMR of 167 was observed for chronic and unspecified nephritis and renal sclerosis. Mortality caused by nonmalignant respiratory disease (NMR) was significantly elevated (SMR at 163). When analyzed by induction/latency period, the SMR for NMR was 278, based on 27 observed and 9.8 expected deaths after 20 years. There was also a 44 percent excess in deaths from accidents. When the risk of death from lymphatic malignancies was analyzed by duration of uranium mill employment, excess risk was limited to the induction/latency period beyond 20 years, with 6 deaths observed versus 2.6 expected. The authors conclude that uranium mining is associated with NMR; however, the data does not support any conclusions regarding the etiology of this hazard.