This chapter describes various published reports of complications in endoscopic sinus surgery. There are minor and major complications that can occur following endoscopic sinus surgery. There are varying number of series published ranging from few hundred to several thousands patients. The type of complication varied from minor bleed to a more serious orbital and intracranial CSF leaks. Some reported series outlines the rate of complication in an experienced and an inexperienced surgeon proving that an adequate training is a very important aspect before embarking upon endoscopic sinus surgery.