The United States spends more on health care than any European country. Previous studies have sought to explain these differences in terms of system capacity, access to technologies, gross domestic product, and prices. We examine differences in disease prevalence and treatment rates for ten of the most costly conditions between the United States and ten European countries using surveys of the noninstitutionalized population age fifty and older. Disease prevalence and rates of medication treatment are much higher in the United States than in these European countries. Efforts to reduce the U.S. prevalence of chronic illness should remain a key policy goal.