Eight patients with breast metastases from primary tumors other than breast carcinoma were studied: 3 malignant melanomas, 2 rhabdomyosarcomas, 1 malignant mesothelioma, 1 appendiceal carcinoid, and 1 epidermoid cervical carcinoma. All had mammographic, histopathologic, and immunohistochemical examinations. The main problem was differential diagnosis from primary breast carcinoma. History of extramammary primary tumor was helpful but breast metastasis was the first clinical feature in 2 cases. Patients had noticed palpable, round, rapid growth masses which were mammographically benign. Pathologic diagnosis was difficult and immunohistochemical studies necessary, whenever the proliferation had histologic features of primary breast carcinoma or when no primary tumor was known. However, some histologic features were of value for diagnosis of metastasis: atypical histologic features for a primary breast carcinoma, a well-circumscribed tumor with multiple satellite foci, the absence of an intraductal component, and the presence of many lymphatic emboli. In adults, the most frequent types of tumors metastasizing in the breast are malignant melanoma and neuroendocrine-like tumors, especially small cell carcinoma and carcinoid. In children, rhabdomyosarcoma is the most common. Accurate diagnosis of breast metastasis is important to avoid unnecessary mastectomy and to implement an appropriate systemic therapy.