This paper considers the path following of unmanned helicopters based on dynamic optimization. We assume that the helicopter is equipped with a flight control system which provides an approximation of its closed-loop dynamics. The task at hand is to derive inputs for this flight control system in order to track a geometrically specified path. A concise problem formulation and a discussion of an efficient implementation is presented. This implementation achieves computation times below the flight duration of the path by exploiting differential flatness of components of the dynamics. Finally, we present quantitative results in respect to convergence and required iterations for a challenging nonlinear path. We show that the proposed optimization based approach is capable of tackling nonlinear path following for helicopters in an efficient manner.