Description: In 1995, Mexico replaced the public pay-as-you-go system by a privately managed system based on individual accounts. This paper analyzes the causes that made necessary the reform of the old Mexican pay-as-you-go pension system. A description of the modifications and current situation of the pension system also are discussed. The paper concludes that although the pension system has been modified during the last few years, there are still some weaknesses that have to be corrected to provide an appropriate retirement benefit to workers.