Genotyping tests for molecular mutations associated with clinical syndromes increasingly allow clinicians to identify health risks before clinical problems occur, sometimes making prevention possible. The clinical use of these tests, however, can create moral problems for families and serious health policy challenges for communities. Those issues, in turn, complicate the professional ethics of genetic testing and counseling. Investigators working with families in gene-identification studies have already encountered these complications in the research setting and their experiences may help in the development of a clinical ethic for genetic testing. In addition to questions about the predictive significance of particular genotypes, three other sets of ethical considerations are becoming important to professional decision-making about genetic testing: the psycho-social impact of testing, the patient’s privileges with respect to testing, and the potential for effective prevention following testing. Underlying all these considerations are basic lessons from the research setting on how clinicians should interpret genetic testing for patients, given the heavily deterministic meanings that they have been taught thus far.