BACKGROUND: Workers exposed to low doses of radiation can provide information regarding cancer risks that are of public concern. However, characterizing risk at low doses requires large populations and ideally should include a large proportion of women, both of which rarely are available. METHODS: Among 90305 radiologic technologists in the U.S. (77% women) who were followed during 1983-1998, data concerning incident cancer occurrence was obtained from mailed questionnaires and from death records. Standardized incidence ratios (SIRs) were computed using age-specific, gender-specific, race-specific, and calendar year-specific cancer rates from the Surveillance, Epidemiology, and End Results Program. RESULTS: The SIR for all cancers in both genders combined was 1.04 (95% confidence interval [95% CI], 1.00-1.07; n = 3292 technologists). Female technologists had an elevated risk for all solid tumors combined (SIR = 1.06; 95% CI, 1.02-1.10; n = 2168 women) and for breast cancers (SIR = 1.16; 95% CI, 1.09-1.23; n = 970 women), melanoma (SIR = 1.66; 95% CI, 1.43-1.89; n = 181 women), and thyroid cancers (SIR = 1.54; 95% CI, 1.24-1.83; n = 107 women). Male technologists experienced a decreased risk for solid tumors (SIR = 0.92; 95% CI, 0.85-0.98; n = 755 men); however, melanoma (SIR = 1.39; 95% CI, 1.00-1.79; n = 56 men) and thyroid cancers (SIR = 2.23; 95% CI, 1.29-3.59; n = 17 men) were increased. Among both genders, the risks were decreased for buccal cavity/pharyngeal cancers (SIR = 0.73; 95% CI, 0.55-0.90; n = 54 technologists), rectal cancers (SIR = 0.62; 95% CI 0.48-0.76; n = 53 technologists), and lung cancers (SIR = 0.77, 95% CI, 0.70-0.85; n = 307 technologists). CONCLUSIONS: The elevated risk for breast cancer may have been related to occupational radiation exposure. The observed excesses of melanoma and thyroid cancers may reflect, at least in part, earlier detection among medical workers with easy access to health care. Copyright 2003 American Cancer Society.