Stereotactic surgery requires knowledge of cerebral structures derived from more than one image source. We have developed a PC-AT-based workstation that accepts patient images, made with the stereotactic frame in place, from CT, MRI, and DSA modalities. Reference markers on the frame are identified in the images to establish the coordinate geometry for each modality. Target points may be identified on each image type and trajectories of probe paths to these points defined. Targets identified on one set of images may be transferred automatically to other images of the same patient in order to guarantee a vessel-free path of approach to a target point deep within the brain. To date several hundred patients have had stereotactic surgery performed on the basis of plans using this system. Procedures included biopsy and aspiration of lesions, implantation of electrodes for the recording of deep EEG signals, and radiosurgical techniques. We present clinical examples of the use of this system in typical stereotactic neurosurgery procedures, address stereoscopic applications, and discuss the results of intermodality tests to establish the accuracy of the technique.