A small-cell carcinoma is one of the histologic subtypes of primary neuroendocrine carcinomas of the breast. A small-cell carcinoma is a rare entity of the breast and exhibits similar morphologic features as neuroendocrine tumors of the gastrointestinal tract and lung. We present the imaging and pathologic findings of a primary small-cell neuroendocrine carcinoma of the breast. This is the first report of a primary small-cell carcinoma arising from the breast in Korea.