The study aimed to determine whether hereditary ovarian cancers that are not caused by BRCA1/BRCA2 constitutional mutations are associated with a predisposition to cystadenoma. The study consisted of two parts. Part one concerned the incidence of ovarian cystadenoma in females from families with hereditary ovarian cancer unassociated with BRCA1 mutations. The study group included 62 female patients from 29 families, without any previously diagnosed malignancy, with no proven constitutional mutation of the BRCA1 gene. The first control group was composed of 62 female patients from 53 families, without any previously diagnosed malignancy, with an identified constitutional mutation of the BRCA1 gene. The second control group comprised 124 female patients for whom the only reason for the examination was a prophylactic check-up. All studied women were subjected to intravaginal ultra- sonographic investigations. In 8 patients with benign and/or borderline ovarian cystadenoma, a complete sequencing of coding fragments of the BRCA2 gene from the peripheral blood DNA was performed. Part two of this study concerned the incidence and pattern of malignant tumors in the families of female patients with ovarian cystadenoma. The final study group included 117 patients who had 726 I0 relatives (359 females and 367 males). We concluded that cystadenoma is likely to be a characteristic feature of the subgroup of families with hereditary ovarian cancers unassociated with BRCA1/BRCA2 constitutional mutations.