Results of several epidemiological studies of workers exposed occupationally to low levels of radiation have been reported but have not included data on smoking. The authors conducted a case-cohort study of male workers at the Hanford Site with an objective of investigating the association between lung-cancer risk and occupational radiation exposure with appropriate adjustment for tobacco use. Eighty-six lung-cancer deaths for the period 1965-1980 and a stratified random sample of 445 subcohort members were included in the study. Tobacco-use data were obtained from medical records collected over each subject's period of employment. Data from this study were analyzed using methods that took into account both the case-cohort design and changes over time in the quality of the tobacco-use data collected. Tobacco use was not strongly related to the level of radiation exposure, and adjustment for tobacco use did not greatly modify results of analyses assessing the association between lung-cancer risk and cumulative dose equivalent. With or without adjustment for tobacco use, the estimated risks per unit of cumulative dose equivalent were negative, but the 95% confidence intervals were wide and included values several times those estimated from populations with high levels of irradiation.