An advanced, third-generation wave model has been repeatly applied to the Mediterranean Sea. We have studied the accuracy of the results and the factors that control it. The grid resolution, when less than 0.5¿, is shown to have in general negligible effect in the open sea. The related accuracy of description of the coastal border can have a relevant effect on the wave field on the side and on the wake of the coastal details, for a distance of a few grid points. The difficulty of correctly evaluating the wind in the Mediterranean basin is dramatically shown comparing the results obtained using wind fields with different resolution. The crucial role of the orography in shaping the wind fields and the need for higher-resolution models is established. It is found that owing to the strong dependence of wave height on wind speed, for resolution coarser than 70 km the loss of accuracy of the wind fields, even if meteorologically acceptable, makes them useless for an efficient evaluation of the wave conditions. The exception, explained by the local absence of relevant mountain ridges, is the case of a southerly wind in the eastern Mediterranean. The accuracy of wave forecasting is obtained by comparing analysis and forecast fields for a very severe storm. In connection with the preferential west to east flow of most of the Mediterranean storms, and with the scarcity of information on the Atlantic Ocean, the equality of the meterological forecast rapidly deteriorates beyond 1 or 2 days of forecase. This lead to an even faster deterioration of the wave forecast, whose practical limits in the western Mediterranean can at present be established at 1 day. ¿American Geophysical Union 1991