A 46-year-old female patient presented with a tumor measuring 0.5 cm in diameter under the areola of the breast. Because no definite malignancy was found with inspection and palpation, imaging analysis, or with a fine-needle aspiration cytology examination, follow-up observation was recommended. When the patient visited the hospital 6 months later, the mass was 0.9 cm in diameter. The tumor was excised and histopathologically diagnosed as a leiomyosarcoma. Subsequently, the patient underwent a partial resection of the breast, including the nipple and areola. A follow-up examination revealed no evidence of distant metastasis or local recurrences 8 years 4 months after the surgery. Primary leiomyosarcoma of the breast is extremely rare. Only 33 cases, which are reviewed in the present study, have been previously reported in the literature.