PURPOSE: Paranasal sinusitis, easily overlooked owing to it's benign symptomatology, should be considered when the upper respiratory tract infction persists longer than seven days. Without early recognition and appropriate management, the disease will take a chronic course and the incidence of complications will be increased. The significance of paranasal sinusitis among Korean children has not appropriately been appreciated; therefore, a clinical study was under-taken to help understand clinical characteristics of paranasal sinusitis in Korean children. METHODS: One hundred sixty five(34.3%), out of 481 patients with no underlying disease seen at the outpatient division of the department of pediatrics, Hanyang university hospital from April 1992 to August 1993, were diagnosed of maxillary sinusitis and included in the study to investigate age and sex distributions, clinical manifestations, radiographic findings, and response to antibiotics therapy. Five patients followed up for less thant two weeks and 45 patients lost in follow up within 3 weeks were excluded in the evaluation of therapeutic response, which were done on the basis of clinical and radiographical analysis. RESULTS: 1) Maxillary sinusitis occurred frequently in young children; among 165 patients, 129 patients(78.3%) were wunder 5 years of age, with 83 patients(50.4%) younger than 3 years of age. The male to female ratio was 1.4:1. 2) One hundred twently three patients(74.5%) had acute sinusitis, 39 patients(23.7%) subacute sinusitis, and 3 patients(1.8%) chronic sinusitis. The most common clinical symptom was cough in 124 patients(75.2%), followed by nasal discharge in 103 patients(62.4%), nasal obstruction in 76 patients(46.1%), and fever in 49 patients(29.7%). The physical finding most commonly observed was postnasal drip in 35 patients(21.2%), followed by otitis media in 21 patients(12.7%), and throat injection in 19 patients(11.5%); however, physical examination was not contributory in 77 patients(46.7%). 3) Radiographic findings on Water's view illustrated opacification in 98 patients(59.4%), mucoperiosteal thickening in 82 patients(49.7%), and air-fluid level in 4 patients(2.4%). Bi-lateral radiographic involvement was 4 times more common than unilateral one. 4) The patients with maxillary sinusitis were trated with amoxicillin(AMX), trimethoprim-sulfamethoxazole(TMP-SMZ)+/-erythromycin(EM), amoxicillin-clavulanate(AMX-CLV) or cefaclor(CCL) in sequence depending on the therapeutic response to each antibiotics. The therapeutic outcome with each antibiotics was 16.3%(15/92) with AMX, 56.7%(51/90) with TMP-SMZ, 70.6%(24/34) with AMX-CLV or CCL. Among 115 patients who have been followed up longer than 3 weeks , 90 patients(78.3%) improved clinically and/or radiographically. Among 90 patients with improvement, 32 patients(35.5%) showed clinical and/or radiographical responses in less than 3 weeks of treatment with effective antibiotics, however 19 patients(21.2%) needed to be treated for longer than 7 weeks. CONCLUSIONS: The data indicated that paranasal sinusitis is a common disease among Korean children, especially in very young ones. Once antibiotic therapy had begun, the follow-up were not infrequently interrupted. The therapeutic response to antibiotics, recommended currently for therapy of paranasal sinusitis, were not good.