In this study, 60 different types of ovarian lesions, mainly consisting of ovarian neoplasms, were studied for the expression of claudins 1, 4, 5, and 7. Strong expression of claudins 1, 4, and 7 was seen in benign and malignant epithelial ovarian tumors. Expression of claudin 5, reported to be mainly present in endothelial cells, was seen in ovarian epithelial tumors, but with a significantly lower frequency than claudins 1, 4, and 7. On the contrary, sex-cord stromal tumors and cysts, such as fibromas/thecomas, Sertoli-Leydig cell tumors, granulosa cell tumors, and follicular and luteinized cysts were mainly negative for claudins 1, 4, 5, and 7. Interestingly, adenomatoid tumors did not express claudin 5, which is in agreement with their non-endothelial nature. They were also negative for claudin 4, but expressed claudins 1 and 7, but to a lesser degree than epithelial lesions. In immature teratomas, the epithelial component was usually positive whereas other components were negative for these claudins. Dysgerminomas did not express any of the claudins studied. The results show that claudins 1, 4, and 7 are mainly expressed in ovarian epithelial tumors and can thus be used to indicate epithelial differentiation in them. Eventhough considered an endothelial marker, claudin 5 was also present in a subset of epithelial lesions. However, this claudin can be used to differentiate adenomatoid tumors from vascular lesions. No significant difference was seen between epithelial benign and malignant lesions, except for claudin 5, which seemed stronger in malignant epithelial tumors.