The ovarian surface epithelium and that of related inclusion cysts were studied in 50 women with ovarian polycystic disease and they were compared with our preceding observations performed on women with endometrial carcinoma (n = 50) and on women without any hyperplastic or neoplastic genital tract pathology (n = 50). In 16 women (32%) the ovarian epithelium with normal aspect was found on the surface of the ovary and in inclusion cysts. In the remaining 34 women (68%) surface papillomatosis, hyperplastic and metaplastic changes were present on the ovarian surface and/or in the inclusion cysts. These findings were similar to those observed in the group of women with endometrial adenocarcinoma, while the surface epithelium was often normal in the control group. Our observations confirm the hypothesis of a hormonal influence in the hyperplastic and metaplastic modifications of the ovarian epithelium and in the related common epithelial tumors of the ovary.