Numerical modelling and HF radar technique are two developing methods for studying coastal circulation. They both have a wide space-coverage, and similar time and space discriminations (respectively a few minutes and a few km 2). It is therefore particularly interesting to compare their results. An experiment using two high-frequency radars was made in Western Baie de Seine at the end of summer 1982, and three days of these measurements, covering a large range of tidal coefficients, have been compared with the corresponding results of a two-dimensional modelling of the whole Bay. Characteristics of this model, as well as the main methodological and technical points concerning HF radar measurements (especially a discussion of the measurements errors, evaluated to be 3 to 7 cm s −1 on each radial component) are presented. A comparison is made at 6 points for the current vector, and at 20 points for one of the radial components. It concerns the half-day mode (amplitude, phase, hodograph). In most of the area, no significant phase lag is observed. The agreement is to within ca. 10 cm s −1 for the amplitude, and to within less than 10° for the bearing of tidal ellipses, with smaller intervals for smaller tides. This agreement shows that the intrinsic accuracy of the model is comparable to that of other sensors such as current meters. What is even more satisfactory is that the model does not use as boundary conditions any measurements specific to the period studied except for sea level forecasts, which are given by a greater scale physical model. A significant difference is observed only close to the coast where the strong gradient of the current velocity (referred to the discrimination scale), is unfavourable both to the model and to the measurements.