Current legislative proposals to increase competition among private insurers assume that people are or can be well-informed about their insurance coverage. Evidence from the National Medical Care Expenditure Survey shows that among the population 65 years of age and older knowledge about health insurance coverage is substantial but generally lower than in the population younger than 65 years of age. Multivariate analysis is used to identify factors associated with high and low levels of knowledge. Although correct knowledge of coverage of particular services is highly associated with current experience of health problems, with use of these health services, and with the cost for private insurance, overall knowledge is lowest among some groups at high risk of serious illness, in particular, the old, nonwhites, and persons enrolled in Medicare but without Medicaid or private insurance supplements.