Most states have enacted genetic nondiscrimination laws in health insurance, and federal legislation is pending in Congress. Scientists worry fear of discrimination discourages some patients from participating in clinical trials and hampers important medical research. This paper describes a study of medical underwriting practices in the individual health insurance market related to genetic information. Underwriters from 23 companies participated in a survey that asked them to underwrite four pairs of hypothetical applicants for health insurance. One person in each pair had received a positive genetic test result indicating increased risk of a future health condition—breast cancer, hemochromatosis, or heart disease—for a total of 92 underwri...