Microscopic intranasal ethmoidectomy has the advantages of stereoscopic and magnified view, operator’s both hands free for surgery and greater familiarity. A retrospective study was done on 371 patients(591 noses) of chronic sinusitis with nasal polyp to analyze the recurrence and complications after microscopic intranasal ethmoidectomy. As the procedure combined with ethmoidectomy, there were 93 cases of sphenoidotomy, which was the commonest. Twenty-four cases(4.1%) had to receive additional operation due to the recurrence, and the recurrence rate was much higher in the group of previous operations and the cases of the removed middle turbinates. Minor complicatios occurred in 21 cases(3.6%), among which the commonest one was the periorbital ecchymosis. 6 cases showed major complications(1%), among which the commonest one was the CSF rhinorrhea(4 cases). As the factors associated with major complications, the operation done by staffs and the cases of the preserved middle turbinates showed significantly lower rate of major complications. Our results suggest that two factors are considered to be very important in order to reduce the major complications. First, surgeons should be careful for surgery in patients underwent ethmoidectomy previously. Second, residents should be intensively trained regarding the detailed surgical anatomy of nasal sinuses and the skillful surgical technique before starting the intranasal ethmoidectomy.