Primary neuroendocrine carcinoma of the breast is an extremely rare neoplasm that differs from other types of breast carcinoma according to the pathological features. We describe here a case of primary neuroendocrine carcinoma in a 72-year-old woman who complainted of a lump in her left breast. After examination and evaluation, the diagnosis was made by a core needle biopsy and the subsequent immunohistochemical examination of the specimen revealed more detailed information. We performed modified radical mastectomy, which showed no axillary node involvement. The patient was given neither radiation nor chemotherapy, however, but hormonotherapy was started postoperatively. Any recurrence has not been demonstrated at 12 months after the operation.