Computer-assisted system for guiding a surgical/diagnostic instrument (27) in the body of a patient wherein a tracking sensor (20) comprises a pair of video cameras/illuminators adapted to acquire the image of a patient (P) on which a surgical/diagnostic operation is being performed by means of an instrument sensed by means of a marker visible by the sensor. The tracking sensor is movable under the thrust of actuators according to a first horizontal tilt axis and a second horizontal pan axis perpendicular to the first to perform a scanning operation of an area of the human body.
