Adenomyoepithelioma of the breast is a rare tumor that, on the basis of histologic, immunohistochemical, and ultrastructural features, has a bicellular pattern of epithelial and myoepithelial cells regularly distributed in tubular structures. Until now, this tumor was thought to be a benign or low-grade malignant lesion because of possible local recurrences (7 recurrent cases of 60 in the literature). Only one of these cases had nodal involvement, thereby suggesting the possible malignancy of this lesion. This paper reports the first documented case of malignant adenomyoepithelioma with lung metastases presenting the same biphasic pattern as the primary tumor.