BACKGROUND Metaplastic carcinoma is a rare form of breast carcinoma that often is confused with other benign and malignant entities. The diagnosis can be difficult to establish on both a clinical and conventional histopathologic basis. One report recently described clinical and mammographic features dissimilar to the authors' experience but to the authors' knowledge no other reports have been published. Therefore a review of three cases was undertaken; all patients had undergone mammography to identify and report the mammographic features of this disease, suggesting that imaging may add to the proper diagnosis of this entity. METHODS Three clinical cases in which the diagnosis of metaplastic carcinoma was confirmed and for which mammography was performed were reviewed retrospectively. Follow-up on all three patients was available. RESULTS Metaplastic carcinoma may be manifest as a well circumscribed mass or an irregular or spiculated mass. The latter always is highly suspicious for malignancy and the former incurs suspicion if it grows, although in this series the smooth mass was biopsied immediately. The spiculated masses were associated with delayed diagnosis and poorer prognosis because immunohistochemical studies were not performed on the original excisional biopsy specimens. CONCLUSIONS Although spiculated masses usually are associated with invasive ductal and lobular carcinoma, they also may represent metaplastic carcinoma and immunohistochemical studies often are required to establish this diagnosis and avoid delay in proper treatment. Well circumscribed masses representing this disease may suggest benign disease but metaplastic carcinoma should be included in the differential diagnosis, especially if the mass enlarges.