This article examines the factors that affect Medicare beneficiaries' choices in the supplemental health insurance market. Data include detailed survey information as well as copies of the health insurance policies owned by a sample of approximately 2,500 Medicare beneficiaries in six states during 1982. Logit analysis is employed to analyze the determinants of four dependent variables: whether a person owns (1) one or more private supplemental insurance policies, (2) two or more policies, (3) at least one policy that we define as "effective," and (4) a policy we define to be "less effective." Those who are better off from a socioeconomic standpoint appear to be making more effective choices in the supplemental health insurance market. However, there does not appear to be a relationship between consumer ignorance or vulnerability and the purchase of multiple supplemental insurance policies. Study results imply an important role for public policy in helping to provide the information necessary to ensure that the most vulnerable beneficiaries make insurance choices that are in their best interest.