According to literature approximately 60% from all ovarian malignances express epithelial phenotype. According to their histomorphological characteristics, epithelial ovarian tumors are divided into eight groups. In some particular cases, separate histological types are hard to distinguish one from another. Recent studies show the presence of beneficial effect of adjuvant radiotherapy on most of the early ovarian carcinomas (all, except serous carcinomas). In renal cell carcinomas SI00A 1 is used to distinguish between different subtypes of the malignancy. Forty cases of ovarian carcinomas were analyzed in a retrospective study. Immunohistochemical evaluation of the S100A1 protein expression was carried out on representative archival formalin -fixed -paraffin-embedded tissue materials. Positivity for S100A1 was observed in 31 (77.50%) of the studied cases. Twenty-seven out of thirty-two (84.38%) cases of serous ovarian carcinoma were found to express S100A1. S100A1 expression was observed in one out of the two mucinous and three out of the six endometroid ovarian carcinomas. Immunopositivity was nuclear, cytoplasmic or nuclear and cytoplasmic in serous carcinomas, nuclear in the one positive mucinous carcinoma and sytoplasmic in the three imunopositive endometroid ovarian carcinomas. The S100A1 immunohistochemical marker is not likely to be useful in clinical practice to distinguish between different histological subtypes of ovarian cancer. The large percentage of S100A1 positivity in serous ovarian carcinomas needs a better understanding.