A numerical modell has been developed at the Department of Meteorology, Uppsala University. The purpose has been to calculate streamline displacements for linear, hydrostatic flow over a three-dimensional hill and to visualize the characteristics of the flow. The model simulates the vertical and lateral displacements and also velocity perturbation fields for flow approaching the hill at constant mean wind and constant stability. The simulations show the lateral deflections, as the air tries to avoid the hill, the horizontal deceleration and ascent upstream and the horizontal acceleration on the lee-slope. Divergence at the mountain top is compensated by descent of air from aloft. Gravity waves propagate upwards and partly outwards along parabolas. It is also shown how linear theory fails to be valid when the Froude number Fr → 1⁺.