This paper discusses some aspects of the seismic behaviour of large homogeneous earth dams. Numerical analyses were carried out using a  plane-strain finite difference model of an existing dam that has been  calibrated using the monitoring data taken during the construction and the impoundment stages. The seismic performance of the dam was evaluated through a series of nonlinear dynamic analyses carried out in the time-domain using four real seismic records applied at the base of the model. The selected input motions are characterised  by the same energy content and  by a very high return period. Both the horizontal and the vertical  component of the seismic action were applied at the base of the grid. In calculations, cyclic excess pore water pressure build-up was accounted for using the  Finn-Byrne model. The  seismic response  of  the  dam  is  discussed  showing  the effects of input motion characteristics and of excess pore water pressure induced by earthquake loading on the maximum permanent settlement developed at the crest, that may be seen as an index of the seismic performance of the dam.