The prediction of susceptibility to heritable breast, ovarian and colon cancer raises important legal and ethical concerns. Health care professionals have a duty to disclose sufficient information to enable patients to make informed decisions. They must also safeguard the confidentiality of patient data. These duties may come into conflict if a positive finding in one patient implies that family members are also at risk. A legal distinction is made between a breach of confidentiality and the legitimate sharing of information in a patient's interest or to prevent harm to a third party. Physicians also have a fiduciary duty to warn. Other issues concern the legal liability assumed by genetic counsellors, whose disclosures may influence decisions about childbearing, for example, and the risk of socioeconomic discrimination faced by people with a known genetic susceptibility. Traditional ethical orientations and principals may be applied to these and other questions, but feminist ethics will likely have particular importance in the development of an ethical stance toward testing and counseling for heritable breast and ovarian cancer.