Malignant mixed mullerian tumor is a rare neoplasm and derives from mullerian mesoderm that differentiates in epithelial and stromal elements. In this case report, pathological and immunohistochemical profile and diagnostic difficulties in malignant mixed mullerian tumor of the uterus were discussed. The case is a 53-year- old patient who complained of pelvic pain and postmenopausal genital bleeding. Computerized tomography was revealed an intrauterine mass measuring 8x5 cm. After the evaluation of the curettage material that was diagnosed as high grade stromal sarcoma; total abdominal hysterectomy, bilateral salpingo-oophorectomy and omentectomy were performed. Histopathologically, the tumor contained squamous cell carcinoma admixed with high grade stromal sarcoma. Additionaly, areas of adenomyosis in the neighbouring of the tumor were noted. Immunohistochemically, malignant stromal cells exhibited diffuse vimentin, smooth muscle actin, myoglobin and focal CD10 and S100 protein positivity. Malignant epithelial cells revealed diffuse positive reaction for epithelial membrane antigen, pancytokeratin (AE1/AE3), vimentin and focal reaction for HCG. A diagnosis of uterin malignant mixed mullerian tumor (carcinosarcoma) with unilateral ovarian and cervix invasion was made. The patient died one week after the pathologic diagnosis because of renal failure. This case is an interesting example of the focal HCG positivity in the malignant epithelial component of the tumor that may represent focal choriocarcinomatous differentiation. Potential relationship between malignant mixed mullerian tumor and adenomyosis was evaluated.