The hydrology of the Bay of Biscay was investigated using the regional ocean model MARS3D (Model for Application at Regional Scale). The simulated hydrology is compared to a set of various data encompassing monthly climatology, remote sensing SST CTD casts, and coastal salinity measurements. Special focus was put on the validation over the continental shelf. This paper reports that despite some misfits, the climatological hydrology and its seasonal variability are correctly simulated. Various statistics computed over the period from 1999-2004 highlight different aspects of the hydrology. The biases and root mean square errors (RMSE) remain very weak at all depths when comparing salinity (< 0.1 and < 0.6psu respectively). The predicted temperature shows a global overestimation of temperature (bias of around 0.8 degrees C) and the maximum errors are located near the thermorcline (rmse of 1 degrees C at 20-40 m). The model is shown to properly reproduce the annual dynamics of sea surface temperature, as well as the dynamics of large river plumes observed by high frequency time series from coastal salinity gauges. The misfits highlighted by these various comparisons between model and observations are attributed to heat fluxes and mixing parameterisation.