The base-isolated University of Southern California (USC) hospital building experienced strong motion during the 1994 Northridge earthquake. California Strong Motion Instrumentation Program data of the response are available for performance evaluation. The objective of this study is to evaluate the seismic performance of the base-isolated USC hospital building during the 1994 Northridge earthquake. A nonlinear analytical model of the USC hospital building is developed and verified using system identification. The response computed, using the presented analytical modeling techniques, is verified using recorded data. Structural behavior during the Northridge earthquake is evaluated in detail. The base-isolated USC hospital building performed well and reduced the response when compared to a fixed-base structure. The free-field acceleration was 0.49g and peak foundation/ground acceleration was 0.37g. The peak roof acceleration was reduced to 0.21g, nearly 50% of the peak ground acceleration. The peak drift was <30% of the code specification. The bearings yielded and dissipated energy (20%). The superstructure was elastic due to the effectiveness of base isolation. The building is expected to perform well in future earthquakes similar to those used in the original design.