An apparatus and method are disclosed for displaying a path between a selected target and selected points on a patient's skull and for guiding surgical instruments along any selected path. The system is comprised of an image display system, an articulated arm and probe, and a stereotactic system. The sub-systems are coupled to one another so that the articulated probe may be used to select patient fiducial points that correspond to selected image fiducial points. Using these points, the image display system coregisters the external locations to the displayed images so that the probe condition may be displayed with the displayed images. The system further permits the identification of a selected target within a patient's brain and to project a path from the external position to the target prior to the performance of a craniotomy. After evaluation of the path, a surgeon may lock the stereotactic system in place to preserve a selected surgical path and to guide instruments along that path. A method of utilizing the system to perform such surgical procedures is also described.