Differential diagnosis is a major problem in histopathology of ovarian tumors. Difficulties may arise if the tumor is a poorly differentiated carcinoma or a granulosa cell tumor of the sarcomatoid type. It was the aim of the present study to evaluate the usefulness of immunohistochemistry in differentiating between granulosa cell tumors of the ovary and ovarian carcinomas. We investigated 56 ovarian malignancies (13 granulosa cell tumors, 17 serous, 14 mucinous and 12 poorly differentiated carcinomas) and performed immunohistochemical detection of Vimentin, Keratin, CA125, CA19-9, CEA, S100 and Ber-EP4. Expression of Vimentin was highest and expression of Keratin was lowest in granulosa cell tumors in contrast to carcinomas. CA125 and CA19-9 were not expressed in granulosa cell tumors, whereas the detection rate in carcinomas (except for CA125 in mucinous carcinomas) was high. CEA, S100 and Ber-EP4 do not seem to be useful markers in differential diagnosis. A marker profile of Vimentin, Keratin, CA125 and CA19-9 allows a quite strict differentiation between poorly differentiated ovarian carcinomas and granulosa cell tumors of the ovary.