An efficient method for the calculation of the inverse dynamic models of tree structure robots is presented. The given method reduces significantly the computational burden such that the inverse dynamics can be computed in real time at servo rate. The method leads almost directly to models with a minimum number of arithmetic operations. The method is based on a Newton-Euler formulation that is linear in the inertial parameters, on an iterative symbolic procedure, and on condensating the inertial parameters by regrouping and eliminating some of them. The description of the robot is carried out by a new notation inspired from Denavit and Hartenberg notation. A Fortran program has been developed to generate automatically the dynamic models of tree structure robots.