While exposure to moderate to high-dose ionizing radiation is an established risk factor for lung cancer, the relationship between lung cancer and chronic low dose radiation remains uncertain. We examined lung cancer risk among 71,894 US radiologic technologists who were certified during 1926-1982, responded to a baseline questionnaire (1983-1989), and were free of cancer other than non-melanoma skin cancer at baseline. Study participants were followed until completion of a second questionnaire (1994-1998), death, or August 31, 1998. We identified 287 lung cancer cases: 66 incident cases and 221 decedents. Exposure to radiation was inferred based on work history information provided in the baseline questionnaire. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazard models adjusted for age, race/ethnicity and smoking. Smoking-adjusted lung cancer risk was not related to working as a radiologic technologist in early years when radiation exposures were likely highest (RR = 0.9; 95% CI, 0.5-1.8 for year first worked before 1940 compared to year first worked >or=1960), nor was risk related to the year first worked after 1940 or the number of years worked in any decade. While lung cancer risk was increased in radiologic technologists who held patients for X-rays, or who allowed others to take numerous practice X-rays on them, the trend was not statistically significant in either case. Although we adjusted for smoking, the possibility of residual confounding exists. Overall, we find very limited evidence that chronic low-to-moderate dose occupational exposure increased lung cancer risk in the US Radiologic Technologist cohort.