In the future there is likely to be a large array of DNA-based tests to diagnose single-gene disorders and to identify predispositions to genetically influenced disorders. This article focuses on ethical, legal, and psychological implications of testing healthy children and adolescents for such disorders. Testing may offer medical or psychological benefits but may harm parent-child bonds or the child's self-concept. Clinicians may encounter situations where they must weigh the child's or adolescent's wishes against wishes of parents. We examine the legal history and current status of minors as health care consumers; psychosocial research on their maturity to make choices; impact of testing on intrafamilial relationships; views of national commissions on appropriate ages of assent and full informed consent; ethical and legal requirements for competence in children and adolescents; and disclosure of genetic information. We propose guidelines for predictive genetic testing and counseling of children and discuss risks and benefits of testing.