Genetic discrimination refers to discrimination directed against an individual or family based solely on an apparent or perceived genetic variation from the "normal" human genotype. We describe here the results of a case history study designed to assess whether or not genetic discrimination exists. Using the above definition of genetic discrimination and applying stringent criteria for case selection, we find that genetic discrimination exists and is manifested in many social institutions, especially in the health and life insurance industries. Stigmatization, and denial of services or entitlements to individuals who have a genetic diagnosis but who are asymptomatic or who will never become significantly impaired, is noted. Follow-up comprehensive studies on the significance and varieties of genetic discrimination are needed. In order to avoid creating a new social underclass based on genetic discrimination (the "asymptomatic ill"), existing and future genetic testing or screening programs need review by medical, scientific, legal, and social policy experts, as well as the public, and may require modification.