The case study of Monticello Dam, proposed as a Blind Prediction in the frame of the USSD Annual Meeting, is adopted to compare results of seismic analysis with measured data. The dam is provided with instrumentation (on foundation and crest), that recorded the acceleration time histories of a low intensity earthquake. Numerical simulations are carried out using the RSE in-house FEM code CANT-SD for the dynamic analysis of dam-reservoir systems, provided with acoustic compressible elements to model fluid-structure interaction and interface frictional elements to simulate the contraction joints. The model is calibrated with a shaking test. The seismic simulation is performed by uniformly applying the acceleration time history to the boundary of the massless rock. The comparison between the results of analysis and the measured data shows that the massless approach leads to a fairly good description of the structural behaviour of the dam, even if slightly conservative.