The challenges of endoscopic sinus surgery lie in the complexity of the anatomy of the nasal vault and side walls and the proximity to critical structures. Additionally, operating in a three-dimensional space while relying on a two-dimensional image for surgical navigation can be a disorienting task. Successful sinus surgery relies on the surgeon having a clear understanding of the anatomy and relationships within the operative field. We performed a study of 8 adult cadaveric heads to better elucidate the location of the ethmoid arteries in relation to an accessible external landmark, the nasal sill. Sinus endoscopy was performed on the heads to identify and measure the distance from the nasal sill to the anterior and posterior ethmoid arteries. We found that the distance from the nasal sill to the anterior ethmoid artery was approximately 6.0 cm, and the distance to the posterior ethmoid artery was approximately 6.7 cm. The interarterial distance was approximately 1.2 cm. With a better understanding of these vessels, surgeons will be better able to avoid them during surgery and thereby minimize the risk of excessive intraoperative bleeding and perioperative orbital hematoma.