In 84 consecutive autopsies of women with a clinical diagnosis of invasive breast cancer, radial scars were found in the contralateral breast in 35 cases (42%) by an extensive histopathologic method. Four women had radial scars on the ipsilateral side in the breast tissue available from the primary surgical procedure or at autopsy. One woman had an invasive breast cancer with morphologic features compatible with but not diagnostic of transition from a radial scar. Of the six radial scars with carcinoma in situ occurring in three women, three were of ductal and three of lobular type. In the remaining cases only radial scars with a benign appearance were found except for two with atypical hyperplasia. The frequency of radial scars was significantly higher in women with fibrocystic disease (55%) compared to women without (24%). Contralateral primary invasive and in situ breast cancer occurred in 68%. No difference in the frequency of radial scars in women with and without breast cancer was found and radial scars were not associated with any specific type of breast cancer. Our findings do not indicate a higher malignant potential of radial scars than of fibrocystic disease. It is suggested that only radial scars containing high-risk epithelial changes such as atypical hyperplasia and carcinoma in situ are associated with an increased risk of subsequent breast cancer development.