ObjectiveTo realize the characteristics of occurrence and distribution of osteoma found in patients undergoing endoscopic sinus surgery (ESS) due to chronic rhinosinusitis with or without nasal polyps (CRSwNP/CRSsNP), and to discuss the surgical strategy for this tumor.MethodsClinical data of 520 adult patients undergoing ESS due to CRSwNP/CRSsNP from Nov. 2006 to Jan. 2010 was analyzed retrospectively. The clinical data included the occurrence and location of osteoma, involvement of lamina papyracea/anterior skull base, surgical strategy for the tumor, surgical complications and so on.ResultsOsteoma was found in 26 of the 520 cases. The occurrence rate was 5% (26/520 cases), with the size of 0.4 cm×0.4 cm×0.4 cm to 1.5 cm×1.5 cm×3.0 cm. Most of them were isolated (23/26) and located in frontal sinus (13 cases) or anterior ethmoid sinus (11 cases). Involvement of anterior skull base and orbital wall was respctively found in 7 and 4 cases. Of all the 26 patients, 20 cases were treated with complete endoscopic resection, 2 with partial endoscopic resection, and 7 without any intervention. All patients had neither immediate nor longterm postoperative orbit/skull base complications.ConclusionsOsteoma is not uncommon in CRSwNP/CRSsNP patients undergoing ESS. This tumor is usually isolated without apparent symptoms and occasionally found in sinus CT. Anterior ethmoid sinus and frontal sinus are most frequently involved. Complete endoscopic resection of the tumor can be achieved in most cases. Under the premise of ensuring sufficient drainage, partial endoscopic resection or nonintervention of the tumor is also acceptable.