This paper presents a real time estimation method of the three dimensional trajectory of a fingertip. Pointing with the finger is indeed a natural gesture for Human Computer Interaction. Our approach is based on stereoscopic vision, with two standard webcams. The hand is segmented with skin color detection, and the fingertip is detected by the analysis of the curvature of finger boundary. The fingertip tracking is carried out by a three dimensional Kalman filter, in order to improve the detection with a local research, centered on the prediction of the 3-D position, and to filter the trajectory to reduce the estimation error.