The aim of this study was to examine whether the principle of “equal treatment in equal need” was met in health care utilization in Korea regardless of income among the elderly. Using data from the Korean National Health and Nutrition Examination Survey for 1998, 2001, and 2005, the authors measured the horizontal inequity of health care utilization and identified the factors contributing to inequality. There were income-related inequalities favoring the better-off for both outpatient and inpatient care utilization among the elderly, for which illness variables and enabling variables of individuals were the most important contributing factors, respectively. In addition, there was horizontal inequity across socioeconomic subgroups in the utilization of both types of care, with significant inequities among the less educated and lower income groups. This study reveals that income-related inequities exist in health care utilization among the elderly and that financial resources are an important determinant of health care utilization despite universal coverage by national health insurance.