The three-dimensional information from computerized tomographic scans has been transformed by image processing for use in stereotactic surgery. A lateral image of the target and calvarium can be superimposed on the lateral x-ray film taken at operation. Computer processing also eliminates extraneous data on the scan and gives the precise distance of the target from the midline. Testing the technique on a phantom shows it to be accurate to better than 0.5 cm. Application of the method for the stereotactic biopsy of a deep tumor is illustrated.