By using intracranial illumination, the surface outlines of the frontal sinuses of 65male Chinese skulls (85 cases) were studied. The frontal sinuses were grouped into 5types according to the relationship of the sinus with the orbit. Three types were visibleon the surface of the squamous portion of the frontal bones (76.5%), whereas the other2 types were only visible intraorbitally (23.5%). Of the 5 types, 4 types of sinuseswere intimately related with the orbit (84.7%). The clinical significance of the above mentioned facts was discussed.