BACKGROUND AND OBJECTIVES: Pediatric endoscopic sinus surgery (ESS) is performed for refractory cases of sinusitis that do not respond to medical management. However, studies evaluating the prognostic factors affecting outcomes of pediatric ESS have not been reported much. The aim of this study is to investigate the prognostic factors affecting the outcomes of pediatric ESS. MATERIALS AND METHOD: A retrospective review of medical records was carried out on 71 patients, 15 years or younger, who had undergone ESS from February, 1995 through January, 2002 at our institution. We classified them into two groups, one with good outcome, and the other with poor outcome, according to the postoperative endoscopic findings. We compared the following 8 parameters between the two groups: presence of allergy, bronchial asthma, adenotonsillar hypertrophy, previous sinus surgery, degree of polyposis, preoperative disease extent scored with OMC CT finding, blood eosinophil count, and eosinophil infiltration in nasal mucosa. RESULT: There were no statistical differences between the two groups on the presence of allergy, bronchial asthma, adenotonsillar hypertrophy, previous sinus surgery, degree of polyposis, preoperative disease extent scored with OMC CT finding, blood eosinophil count, and eosinophil infiltration in nasal mucosa. CONCLUSION: Prognostic factors affecting the outcome of pediatric ESS are not clear. We assume that postoperative care, including appropriate postoperative medication, debridement and irrigation, etc., is more important in pediatric ESS.