Although increased mortality from diseases of the circulatory system has been observed in patients treated with radiotherapy, the effects of chronic low-dose radiation exposure are not clear. Among 90,284 US radiologic technologists who responded to a mailed questionnaire during 1983-1989, the authors evaluated mortality from circulatory system diseases through 1997 in relation to job history and work procedures as surrogates for radiation exposure. They used Poisson regression models stratified for sex, race, age, and calendar year and adjusted for smoking, body mass index, alcohol intake, marital status, parity, menopausal status, and history of myocardial infarction. A total of 1,107,100 person-years accrued, and 1,070 subjects died from circulatory system diseases. Relative risks for first employment during 1950-1959, 1940-1949, or before 1940, compared with 1960 and later, were 1.01 (95% confidence interval (CI): 0.78, 1.30), 1.14 (95% CI: 0.86, 1.50), and 1.42 (95% CI: 1.04, 1.94), respectively (trend p < 0.001). For the subset of deaths from cerebrovascular disease (n = 174), the respective relative risks were 0.90 (95% CI: 0.45, 1.78), 1.54 (95% CI: 0.74, 3.23), and 2.40 (95% CI: 1.09, 5.31) (trend p = 0.004), and for deaths from ischemic heart disease (n = 633), the relative risks were 0.98 (95% CI: 0.71, 1.35), 1.00 (95% CI: 0.71, 1.42), and 1.22 (95% CI: 0.81, 1.82) (trend p = 0.026). The relative risks for mortality from circulatory system diseases and the subset of cerebrovascular disease increased significantly with the number of years worked before 1950 (trend p = 0.007 and < 0.001, respectively). The data suggest increased mortality from diseases of the circulatory system with occupational radiation exposure before 1950 when radiation doses were likely high.