BACKGROUND: The greater palatine foramen injection is effective for minimizing bleeding during sinus surgery. The correct depth is important to minimize risk of orbital penetration. This study analyzed the length of the greater palatine canal using high-resolution computed tomography (HRCT). METHODS: HRCT sinus scans from 100 adults were analyzed. One thousand two hundred measurements were performed by three observers. RESULTS: The mean distance of the greater palatine foramen to the orbital floor was 40+/-3 mm in men and 37+/-3 mm in women (range, 32-46 mm). The mean distance of the greater palatine foramen to the sphenopalatine foramen was 28+/-2 mm in men and 27+/-2 mm in women (range, 23-33 mm). CONCLUSION: The greater palatine foramen injection is an appropriate method to minimize bleeding during endoscopic sinus surgery. The authors recommend an injection depth of 25 mm in adults to minimize the risk of intraorbital complications.