American families are a segment of the public that will feel the impact of the Human Genome Project most acutely: but they are also one of the least well studied segments with regard to that impact. Three sets of ethical problems, in particular, deserve more scrutiny: the effect of increased genetic risk assessment on family members’ willingness to assist their kin discover mutually incriminating genetic risks, its impact on the candor with which extended families communicate within themselves about their genetic health risks, and its influence on the ways that families seek to protect the interests of their most vulnerable members. In each of these areas, anecdotal experience already shows how genetic testing can undermine a family’s commitment to its own interdependence in these ways, and that traditional, multigenerational, sessile families are likely to experience more disruption than either blended families or “virtual families” linked primarily through electronic communication.