To define anatomical relationships relevant to stapes surgery, computer-aided three-dimensional reconstruction and measurement were performed on nine normal temporal bones. The mean distance from the inferior portion of the long process of the incus to the center of the oval window was 3.80 mm. The shortest distance from the center of the oval window to the utricular macula, saccular membrane, and macula averaged 1.37, 1.60, and 2.13 mm. Surgery directed posteromedial-superior from the oval window was found to be most dangerous because it would come so close to the utricular macula; a posteromedial-inferior approach was found to be safest. The distance from the inferior margin of the oval window inferiorly to the cochlear duct in the hook portion ranged between 0.58 and 1.29 mm, suggesting that when a drill hole is made on the inferior margin of the oval window to lift up a depressed stapes footplate, the hole should not be greater than 0.5 mm in diameter.