Among 83 consecutive, unselected female autopsy cases, 6 had been treated for invasive breast carcinoma (IBC) during lifetime. At autopsy, of these six women, two had IBC in the contralateral breast, and another two had in situ carcinoma. Among the 77 women without previous clinical breast cancer, one case of IBC and 14 cases of in situ carcinoma were found at autopsy. Thus, the total occurrence of primary malignant breast lesion was as high as 25.4%. Assuming that all IBCs evolve from in situ forms and that in situ carcinomas do not undergo total regression, our results seem to indicate that about one third of all in situ carcinomas develop into IBC.