Complications of endoscopic and classic intranasal sinus surgery have been documented by case reports and large retrospective reviews. The most serious complications have involved violation of the intracranial space or orbit. Hemorrhage has also proven to be a significant cause of morbidity, either of itself, or by limiting visualization and thus contributing to other injuries. Although numerous studies have been performed to determine various anatomic relationships, relatively few have addressed relationships that use practical reference points easily accessible to the endoscopic or intranasal sinus surgeon. In an effort to reduce the risk of complications such as blindness, orbital hematoma, and injury to the lacrimal sac or central nervous system, we have performed 50 cadaver dissections and measured 7 anatomic landmarks that may aid the surgeon in preventing these complications. We have also included a review of the literature concerning the complications of endoscopic and intranasal sinus surgery addressed herein.