목적: FESS is a technique aimed to treat pathology in the nose and paranasal sinuses safely and efficiently. This technique is not without complications . Mosher, 1929 stated that it might be the easiest way to kill a patient. A 1990 survey of nearly 7000 American otolaryngologist showed 0.5% incidence of CSF leak for endoscopic ethmoidectomy, whereas orbital complications was significantly lower. Kennedy et.al, 1994. it is possible minimize complications with good knowledge of anatomy & radiology, Learning curve, good patient selection surgery. 방법:Retrograde collection of the various complications during FESS practice average numbers (8500 cases) by the same surgeon (the author) from 1998 to 2015. 결과:We reported few complications during our FESS practice like CSF leak, orbital complications, bleeding, synechia... and how we deal with them. 결론: It is possible to minimize complications during FESS with good knowledge of anatomy & radiology, Learning curve and good patient selection surgery.