February 1997 Ukraine's pension system requires radical reforms to restore credibility to the system and remove distorted incentives that make it unsustainable. Resumption of growth alone will not solve the current difficulties. In recent years -as a result of economic contraction, declining employment and real wages, and changes in labor market behavior- Ukraine's tax base of the social security system has declined, threatening its sustainability. About 40 percent of the labor force works in the informal sector, paying no taxes, and many members of the formal workforce underpay taxes because they also do informal work. Using a model that links the social security system, the labor market, and the macroeconomy, the authors ran simulations to assess the sustainability of the current pension system and the relevance and viability of possible reforms. All simulations assume economic reform and the resumption of growth. They conclude: (1) Economic contraction is not the only cause of problems with the pension system. To reverse current trends, most of the labor force would need to be working in the formal sector -an unlikely event, given current incentives. (2) Reform is essential. Restoring the former system would be too costly, and maintaining the status quo would make the system unsustainable. ((3) Reforms focusing on short-term budgetary effects and neglecting the interactions between the social security and the labor market are likely to fail. (4) Raising the retirement age to 65 would have a significant financial impact, but would need to be accompanied by deeper structural reforms. Raising the retirement age quickly may entail the least political cost, as many old people are currently working. (5) For the deeper structural reforms needed, introducing a funded-tier should be considered. It would be an effective way to correct distortions and restore credibility. (6) Introducing such reforms will be costly and affect several generations of workers and pensioners in different ways. Tradeoffs must be carefully evaluated. This paper--a product of the Country Operations Division 2, Country Department IV, Europe and Central Asia Region--is part of a larger effort in the region to foster pension reforms. The study was funded by the Bank's Research Support Budget under research project Social Safety and Growth: An Analysis of Interactions and Tradeoffs (RPO 680-35).