A new method for the estimation of ego-motion (the direction and amplitude of the velocity) of a mobile device comprising optic-flow and inertial sensors (hereinafter the apparatus). The velocity is expressed in the apparatus's reference frame, which is moving with the apparatus. The method relies on short-term inertial navigation and the direction of the translational optic- flow in order to estimate ego-motion, defined as the velocity estimate (that describes the speed amplitude and the direction of motion).A key characteristic of the invention is the use of optic- flow without the need for any kind of feature tracking. Moreover, the algorithm uses the direction of the optic-flow and does not need the amplitude, thanks to the fact that the scale of the velocity is solved by the use of inertial navigation and changes in direction of the apparatus.