The principal objective of this study is to evaluate the cost-effectiveness as well as the seismic safety of a base isolated building located in Peru. A methodology to evaluate quantitatively the seismic risk and the cost-effectiveness of a base isolated building during its lifetime is presented. The process starts with the hazard analysis and the earthquake ground motion generation in the studied area. Lima area is considered in this study. Series of artificial earthquake ground motions are generated by a stochastic method in the studied area. Then a preliminary seismic design of the target building is carried out, by using the Peruvian seismic code. To get the response distribution of the target building, several dynamic nonlinear analyses are performed by using the generated artificial motions as input waves. By assuming a structural response distribution, the seismic risk analysis is performed in terms of three structural parameters such as: interstory drift ratio (IDR), floor acceleration (FA) and the structural damage index (Dl). The damage of the target building is evaluated by using damage index. Finally, the cost-effectiveness of using base isolation system is examined, by comparing exceendance probability of repair cost in the target building with and without base isolation during a given time period.