Problems are often encountered in the diagnosis of chronic maxillary sinusitis which is familiar disease in ENT practice. Chronic maxillary sinusitis is not curable properly but recurres frequently by conservative treatment without surgical measures. The symptoms and signs resemble very much those met in other upper respiratory tract infection. Hardly any symptom can be considered typical enough to be diagnostic and even the signs can be confusing. Because of its clinical difficulty, precise diagnosis is important in treatment of chronic maxillary sinusitis. Radiologic opacification of the maxillary sinus has usually presented a dilema for the clinician in the evaluation of the patient with symptoms and signs of maxillary sinus disease. A-mode ultrasound, however is simple diagnostic tool that can be used to confirm the presence of fluid within the maxillary sinus, and to differentiate solid tumor or mass from a fluid filled sinus, both of which may present with similar radiographic appearances. Patients with thickened mucous membrane indicative of chronic sinusitis can also be identified with this simple nonionizing modality. The reliability of A-mode ultrasound in locating the presence of localized fluid collections, as well as in differentiating cystic form solid masses throughout the body, has been well documented. Its usefulness in the evaluation of the maxillary sinus has not been accepted gained with acceptance. This article demonstrates the diagnostic reliability of A-mode ultrasound compared with radiologic findings on the basis of 68 cases' operative findings. The result was as follows. 1) 12 cases of normal X-ray and ultrasonographic findings were excluded among 80 cases of maxillary sinuses in 40 patients. 2) In the series of 16 cases of maxillary antrum puncture and irrigation, 8 cases represented secretion in 15 cases of abnormal X-ray findings, and 8 cases represented secretion in 13 cases of abnormal ultrasonographic findings. 3) 1 case of normal X-ray finding with abnormal ultrasonographic finding, and 3 cases of normal ultrasonographic findings with abnormal X-ray finding represented no secretion when maxillary antrum puncture and irrigation. 4) Secretion was represented in the 6 cases of 9 cases X-ray findings of secretion, and in the 6 cases of 7 cases of ultrasonographic findings of secretion represented secretion when maxillary antrum puncture and irrigation. 5) In the series of 52 cases operative findings of Caldwell-Luc's operation were divided into subgroup and it was compared with X-ray and ultrasonographic subgroup findings. The agreement was 35 cases with X-ray findings, and 34 cases with ultrasonographic findings. 6) Abnormal operative findings were represented in 3 cases of 4 cases normal X-ray finding with abnormal ultrasonographic finding, and 2 cases of 3 cases normal ultrasonographic finding with abnormal X-ray finding during Caldwell-Luc's operation. 7) The confidence rates of X-ray and ultrasonographic finding were 66.7%, 85.7%, respectively with maxillary antrum puncture and irrigation, and 67.3%, 65.4% with Caldwell-Luc's operation. The difference was not stastically significant(p>0.05).