Malignant adenomyoepithelioma of the breast is a rare lesion characterized by malignant proliferation of epithelial and myoepithelial cells that show characteristic histologic and immunohistochemical features. Eleven cases have been reported, 4 of which showed evidence of distant metastasis. The authors report a case of malignant adenomyoepithelioma in the axillary tail of a 71-year-old woman, one of the oldest patients described so far, and review the literature. Malignancy in the current case was evidenced by the presence of local invasion, high mitotic rate, and severe cytologic atypia. The tumor was associated with adenosis and lobular adenomyoepithelial hyperplasia. Malignant adenomyoepithelioma is a rare neoplasm, diagnosable by light microscopy and immunohistochemistry. To date, it has only been reported in women, who ranged in age from 26 to 76 years. Metastases have only been documented in tumors 2.0 cm in diameter or larger.