Abstract. Variational methods for optic flow computation have the reputation of producing good results at the expense of being too slow for real-time applications. We show that real-time variational computation of optic flow fields is possible when appropriate methods are combined with modern numerical techniques. We consider the CLG method, a recent variational technique that combines the quality of the dense flow fields of the Horn and Schunck approach with the noise robustness of the Lucas–Kanade method. For the linear system of equations resulting from the discretised Euler–Lagrange equations, we present a fast full multigrid scheme in detail. We show that under realistic accuracy requirements this method is 175 times more efficient than the widely used Gauß-Seidel algorithm. On a 3.06 GHz PC, we have computed 27 dense flow fields of size 200 × 200 pixels within a single second.