Advances in genetic technologies raise a multitude of ethical issues, some of which give rise to novel dilemmas for medical practice. One of the most controversial problems arising in clinical genetics is that of confidentiality and who may disclose genetic health information. This paper considers the question of when it is appropriate for health professionals to disclose clinically significant genetic information without patient consent. Existing ethical principles offer little guidance in relation to this issue. We build on suggestions that genetic (...) information may be viewed as collective or shared information, and we introduce the concept of ‘familial comity’ as a fresh way to consider the issues. (shrink)