OBJECT: There is a lack of reports in the literature that contain descriptions of superficial anatomical landmarks for the identification of the internally located frontal sinus. Neurosurgeons must often enter the cranium through the frontal bone and knowledge of the frontal sinus is essential to minimize complications. METHODS: Seventy adult cadaveric frontal sinuses were evaluated. Measurements included both the lateral and superior extent of the frontal sinus in reference to a midpupillary line, and the superior extent of the frontal sinus from the nasion. Frontal sinuses were found bilaterally in all specimens. The mean height of the frontal sinus superior to the nasion was 2.8 cm. In 71.4% and 74.3% of specimens the lateral extent of the frontal sinus was found to be medial to the left and right midpupillary line, respectively. Distances superior to a plane drawn through the supraorbital ridges at a midpupillary line included a mean of 2.5 mm for the left side and 1.8 mm for the right side. CONCLUSIONS: Of 70 sinuses, none extended more than 5 mm lateral to a midpupillary line. At this same midpupillary line and at a plane drawn through the supraorbital ridges, the frontal sinus was never higher than 12 mm. Finally, in the midline the frontal sinus never reached more than 4 cm above the nasion. These measurements will assist surgeons who must manipulate the frontal bone.