A rare case of invasive histiocytoid breast carcinoma is presented. A middle aged female patient underwent quadrantectomy for a palpable mass in her right breast. The neoplastic cells showed pronounced histiocytoid appearance and immunopositivity for cytokeratins 7 and CAM 5,2, EMA, CEA, GCDFP-15, MFG and ER/PR. We report here this uncommon histologic pattern because of the considerable diagnostic interest. Recognition of this histologic variant either in primary or metastatic locations may present some difficulties to the pathologist. Differential diagnostic problems are emphasized and the literature is reviewed.