Our study examined 166 patients with breast cancer with a mean age of 63 years. Each patient underwent mastectomy with the organ being investigated by histological giant sections and additional small sections from the nipple. Nipple involvement was found in 64 cases (38%). Multifocal carcinoma occurred in 76 patients. Further multicentric carcinomatous foci (36 cases) demonstrated a significant increase in affected nipples. Additional atypical ductal or lobular hyperplasia was observed in 53 cases and showed involvement in 34. Nine carcinomas of ductal origin were combined with lobular carcinoma in situ, all cases proved to have carcinomatous changes in the nipple. It is concluded that apart from the well-known influence of advanced tumor stages and tumor localization, nipple involvement correlates with multicentricity and multifocality of breast cancer as a disease of the whole organ.