About 5% of all ovarian-cancer cases are caused by a genetic predisposition, in particular as a component of the autosomal dominant hereditary breast-ovarian-cancer syndrome. This syndrome is usually due to germline mutations in the BRCA1- or BRCA2-gene. Ovarian and endometrial cancer also occur in families with hereditary non-polyposis colorectal cancer (HNPCC). This syndrome is caused by germline mutations in DNA mismatch-repair genes. Women at high risk of gynaecological cancer based upon familial clustering of disease or a demonstrated pathogenic germ-line mutation are candidates for surveillance: annual gynaecological examinations, including vaginal echoscopy and serum carcinoma antigen CA125 testing. Prophylactic surgery in the form of adnexectomy leads to a marked, but not complete, reduction of ovarian-cancer risk in high-risk cases. There is insufficient evidence to advise against the use of oral contraceptives or hormonal substitution after adnexectomy for healthy women with a genetic predisposition to breast cancer. Recommendations for surveillance and prevention should only be given after genetic-risk counselling, based on a detailed family study and DNA-based diagnosis.