Context Patients choosing to retain the nipple when undergoing therapeutic or prophylactic mastectomy are at risk for cancers arising at that site. Objective To identify cases of invasive carcinoma arising within the nipple and to investigate their clinical, imaging, biologic, and staging features. Design Carcinomas were identified by prospective review of surgical and consult cases at 4 hospitals. Results The 24 patients identified presented with symptoms related to the nipple. Mammography did not detect the cancer in most cases. Ten patients (42%) had skin changes from ductal carcinoma in situ involving nipple skin (Paget disease), with small foci of invasion into the dermis, and 6 of those 10 carcinomas (60%) stained positive for human epidermal growth factor receptor 2 (HER2). The remaining 14 patients (58%) presented with a nipple mass or with skin changes. These were larger invasive carcinomas of both ductal and lobular types. Only 2 of those 14 carcinomas (14%) were HER2+. Three of 15 patients (20%) undergoing lymph node biopsy had a single metastasis. No patients have had recurrent disease. Conclusions Rare, invasive, primary nipple carcinomas typically present as subtle nipple thickening or an exudative crust on the skin. Imaging studies are often nonrevealing. A variety of histologic and biologic types of carcinomas occur, similar to cancers arising deeper in the breast. Although the carcinomas invaded into the dermis, some with skin ulceration, the likelihood of lymph node metastasis was no higher than carcinomas of similar sizes. Patients who choose to preserve their nipple(s) should be aware of the possibility of breast cancer arising at that site and to bring any observed changes to the attention of their health care providers.