This study was made to evaluate a modified surgical technique for endoscopic removal of the antral portion of antrochoanal polyp (ACP) by powered instrumentation. 1lventy patients with ACP (12 male and 8 female patients; age range, 13·50 years: mean age. 14.8 years) were included in this study. All patients had unilateral ACP and underwent ESS by powered instrumentation. The usual technique ofESS was performed. The intranasal portion of ACP is removed and the natural ostium oj the maxillary sinus is enlarged. to obtain a good surgical view oj the sinus. A trocar consisting oja cannula and a sheath is inserted sublabially into the maxillary sinus through the canine Jossa. and the cannula is removed, leaving the sheath in the canine Jossa. A 4-mm. 300 endoscope is inserted into the maxillary sinus through the sheath to examine the interior oj the sinus. After careful observation of the maxillary Sinus. the endoscope and the sheath are reo moved. and a cutter blade ojpowered instrumentation is inserted into the Sinus through the hole created by the above-mentioned procedures The blade tip is identified through the enlarged ostium under intranasal endoscopy using a 700 endoscope. Then the antral portion oj the ACP is resected by powered instrumentation. When all steps oj surgery are completed. nasal packs are placed in the nasal cavity Jor .1 day.