The paper deals on a significant retrofit project currently under construction of an existing hospital building in Avellino (Italy). The seismic retrofit was realized by connecting the first floor of the three existing structures and creating one only isolation system composed of high damping rubber bearings and sliding devices. The base-isolation is achieved by gradually cutting the building from foundation and installing the isolators at the level of upper edge of the columns. The study allowed the verification of the adequacy of the isolation system, showing the benefits of the application of the isolation devices, the limitations and the characteristics of their performance.