In the present study, the anatomic location of supraorbital and greater occipital nerves and their branches was quantitatively determined with regard to halo pin placement, and a safe zone for anterolateral and posterolateral halo pins was defined to minimize neurologic damage. The mean distance between the midline and the lateral branches of supraorbital nerve and greater occipital nerve was 3.9 +/- 0.4 cm and 4.8 +/- 0.6 cm on the left side and 3.9 +/- 0.5 cm and 4.8 +/- 0.6 cm on the right, respectively. The mean angles of lateral branches of supraorbital and greater occipital nerves with respect to sagittal plane were 26.0 degrees +/- 6.0 degrees and 38.0 degrees +/- 5.0 degrees on the left side and 25.0 degrees +/- 4.0 degrees and 38.0 degrees +/- 4.0 degrees on the right, respectively. The supraorbital and greater occipital nerves and their branches are safe when the halo pins are placed at sites 4.5 cm and 6.0 cm lateral to the anterior and posterior midlines.