In 40 breasts with primary carcinoma, the nipple and areola were cut horizontally in order to investigate the frequency of intraductal and invasive cancer. In 20 of these breasts the nipple and/or areola were found to be involved at a depth of 1 cm (50%; 95% confidence limits: 33.8–66.2%). Eleven neoplasms were purely intraductal, eight intraductal as well as stromal, and only one purely stromal. By means of clinical or physical findings, it was not possible to select the breasts in which the nipple and/or areola were not involved. It is concluded that the general use of surgical methods preserving the nipple and areola in treating breast cancer leaves a focus of invasive or intraductal carcinoma in about half the patients. The implications of this are not known.