An association between low-dose diagnostic X-ray exposure or therapeutic radiation treatment and breast cancer risk has not been established. To further investigate the issue, we analysed data from a case-control study of breast cancer in Connecticut in 1994-1997. A total of 1217 subjects (608 breast cancer cases and 609 controls), 30-80 years old, participated in the study. A standardized, structured questionnaire was used to collect information through in-person interviews on diagnostic or therapeutic radiation and other breast cancer risk factors. An odds ratio (OR) of 1.7 (95% confidence interval (CI) 0.8-3.6) was observed for postmenopausal women with therapeutic radiation treatment for skin problems such as ringworm and acne, and an OR of 2.5 (95% CI 1.0-6.8) for those who reported having been treated six or more times. Radiation treatment received at younger ages seems to carry a higher risk. In earlier studies therapeutic radiation for skin problems has been associated with an increased risk of breast cancer. Therefore, it is possible that scattered radiation from these treatments could increase the risk of breast cancer. Radiation exposure from diagnostic X-rays was not associated with a significantly increased risk of breast cancer in this study.