In this article, the analysis of inequalities in health care utilization, produced by the taking out of a private health insurance policy to supplement the care provided by the Spanish National Health System, has been performed by the Oaxaca-Ransom decomposition. Using the European Community Household Panel, this method permits the conclusion that the majority of differences in the number of visits to a general practitioner are explained by the individual characteristics of the publicly insured, while the divergences in the number of consultations with specialists are the result of the overuse of this care by the population with double health insurance coverage.