The BRCA1 breast-ovarian cancer susceptibility gene was identified recently. Germline mutations in BRCA1 may be responsible for as many as 5% of breast and ovarian cancers. Inherited alterations confer up to a 94% risk of developing breast and/or ovarian cancer by age 70. With the discovery of BRCA1, there will be a heavy demand for genetic testing. Because of the large size of the gene and the distribution of reported mutations, scientists face considerable technical problems in developing widely available screening tests; clinicians will face even greater ethical problems in applying them. In the context of research programs, women with BRCA1 mutations are already being identified, and their physicians are confronted with a number of complex medical, ethical, legal, and social issues. Obstetricians will be faced with counseling parents regarding prenatal testing for specific BRCA1 mutations. Although it is difficult to formulate straightforward guidelines regarding prenatal BRCA1 testing, clinicians and health care providers must be familiar with the nuances of the debate so that these issues can be discussed wisely with patients. As with many ethically challenging problems in medicine, individual clinicians and their patients will have to work together to determine the course of action with which they are most comfortable. Although elective termination of a pregnancy with a germline mutation in BRCA1 is an option, experience with other adult-onset diseases suggests that only a minority of parents will choose this option.