Chronic rhino sinusitis (CRS) is a common condition in medical practice, which affects many people worldwide and its prevalence is rising. Endoscopic sinus surgery (ESS) has evolved as an effective surgical treatment option for medically refractory CRS with excellent success rates. Successful endoscopic sinus surgery requires a thorough knowledge of the anatomy in particular the relationship of nose and sinuses to adjacent vulnerable structures such as the orbit or base of the skull. Endoscopic sinus surgery, like traditional sinus surgery, is associated with serious risks. Major surgical risks in EES include partial loss of vision or blindness, diplopia, damage to the cribriform plate or to the roof of the ethmoid sinuses, and injury to the internal carotid artery in the wall of the sphenoid sinus. As an entire generation of otolaryngologists learns these new techniques, other complications will emerge. Prevention begins with proper endoscopic and preoperative CT evaluation and surgical preparation.