Treatment of chronic paranasal sinusitis (CPS) by functional endoscopic sinus surgery refers to removal of the pathologic tissue which interferes with the physiologic function of the sinuses in the ostiomeatal complex under direct vision by use of endoscopes to restore the ventilation and drainage of the sinuses. While the ventilation and drainage of the sinuses become normal, the lesions of sinus mucosa will recover spontaneously and the function of the sinuses will be restored. From May to August 1988, functional endoscopic sinus surgery was performed in 47 cases based on the operative methods described by Dr. Stammberger. We excised the uncinate process of middle meatus and entered the infundibulum. The pathologic tissue in the frontal recess was removed first. The anterior ethmoid sinus and posterior ethmoid sinus were cleared depending on the excisable extent of the lesion and the sphenoid sinus wound be opened if necessary. Middle meatal antrosomy was finally performed to enlarge the obstructed ostium of the maxillary sinus. Seventeen of them met the criteria: 1. a history of the disease for more than 3 months and not improving or recovering after medical treatment 2. no past history of surgical treatment for CPS 3. the etiology is not dentigerous or septal deviation. Because one patient lost to follow up, sixteen patients constituted the materials of this study. About 80% of patients were improved or asymptomatic. No serious complication occurred in all patients and the most common one was the adhesion between the middle turbinate and the lateral nasal wall.