In this study, the authors investigated the short-term (i.e., 1-yr) health effects of low-level occupational and personal exposure to ionizing radiation in a hospital setting. Thyroid function, lung function, platelet count, and leukocyte classification were obtained for 142 ionizing radiation operators. In addition, individual exposure doses were measured. The mean annual cumulative dose in 25 exposed subjects was 6.0 +/- 10.1 millisieverts. The highest exposure ratio among 20 of 41 (49%) radioisotope operators was significantly higher than for other ionizing radiation workers. Abnormal leukocyte counts occurred in 26% of radio-diagnosis operators and 30% of radioisotope operators, compared with 15% for other potentially exposed operators. No significant relative risk was found in subjects with above-background exposures. However, the highly exposed population experienced elevations in thyroid stimulating hormone (adjusted odds ratio [ORa = 2.0; T3 [OR = 1.7]); mononuclear leukocytes (ORa = 2.4); and basophilic leukocytes (ORa = 2.0). Although the authors failed to find short-term health effects in hospital operators exposed annually to less than 6.0 millisieverts of ionizing radiation, additional protection would certainly be prudent for these operators.