Epidemiologic data support the existence of two discrete manifestations of hereditary ovarian carcinoma: the breast and ovarian cancer syndrome and the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome. Genetic linkage analyses reveal that the majority of breast and ovarian cancer families are linked to the BRCA1 gene, while some cases of hereditary ovarian cancer are also apparent in breast cancer families linked to the BRCA2 gene. The majority of HNPCC families are linked to one of four genes encoding a family of DNA mismatch repair proteins. Molecular analyses demonstrate that genetic screening for germline transmission of a defective allele of one or another of these genes is now possible for high-risk individuals. The ethical, legal, and social implications of this type of analysis are multiple and complex, and genetic counseling requires a thorough understanding of these issues and a cautious approach to most effectively meet the special needs of this patient population. Increased medical surveillance and prophylactic oophorectomy are among the management options that may be appropriate for some genetically predisposed, asymptomatic women. Further research is needed regarding the most effective use of this genetic information in formulating counseling and clinical management strategies.