We have combined three-dimensional (3D) computer-reconstructed neuroimages with a novel video registration technique for virtual reality-based, image-guided surgery of the brain and spine. This technique allows the surgeon to localize cerebral and spinal lesions by superimposing a 3D-reconstructed MR or CT scan on a live video image of the patient. Once the patient''s scan has been segmented into the relevant components (e.g., tumor, edema, ventricles, arteries, brain and skin), the surgeon studies the 3D anatomy to determine the optimal surgical approach. The proposed intraoperative surgeon''s perspective is displayed in the operating room at the time of surgery using a portable workstation. The patient is then brought to the operating room and positioned according to the planned approach. A video camera is trained on the patient from the proposed intraoperative surgeon''s perspective. A video mixer merges the images from the video camera and the 3D computer reconstruction. This video mixer can vary the output intensity of the two input images between 100% of either and 50% of both. This visually superimposes the two images, not unlike a photographic double exposure. The patient''s position and the 3D reconstruction are then adjusted until the images on the video mixer''s output monitor are identical in terms of scale, position and rotation. This superimposition is facilitated by aligning various surface landmarks such as the external auditory canal, lateral canthus, and nasion. In some cases, such as with spinal tumors, capsules placed on the skin prior to scanning serve as fiducials. After alignment of the video and computer skin images, the computer image of the skin is selectively deleted leaving the 3D image of the underlying brain or spine superimposed on the video image of the patient''s skin. The borders of the tumor and important cortical sulci or spinal anatomy may then be outlined on the patient''s skin using indelible markers. These markings allow the surgeon to plan an adequate opening with minimal exposure of adjacent structures. So far we have used this technique to localize seven brain tumors and one intradural, extramedullary spinal tumor. In addition, the same technique was used to guide the repositioning of the bones in a reconstructive craniofacial surgery. In each case we found excellent correlation between the operative findings and the predicted anatomy. No patients suffered any permanent neurologic deficit.