Sinoscopy as an endoscopic investigation method of the maxillary sinus offers the advantage of a direct local interpretation in contrast to the usual indirect methods. The beginnings of sinoscopy go back to Hirschmann(1903) and Spielberg (1922). During the last 20 years, the methods has been reintroduced and the technique has been refined. In spite of large numbers of articles about sinoscopy in Europe, there is no article about sinoscopy from Korea. In the present study, 182 maxillary sinuses were examined by sinoscopy and PNS X-ray for diagnostic reasons. Our failure rate in sinoscopy was 3.8% and the rate of incomplete sinoscopy was 7.7%. In the evaluation of maxillary antral mucosa, sinoscopy was superior to X-ray. Incorrect evaluation of discharge in the maxillary sinus by 3 standard projections was 78.9%. But as the decubitus Waters' view was added, the incorrect evaluation by X-ray became 20% in the demonstration of discharge in the maxillary sinus. There was usually a 5.8 day time interval between sinoscopy and X-ray examination because of scheduling problems. In the bacteriological study of antral secretions, the percentage of no growth specimens was 75.7%. In all about ten strains of bacteria were isolated from the secretions. Among them, streptococcus was the most common organism. Therapeutic sinoscopy was performed in 16 patients who suffered from subacute or chronic maxillary sinusitis. Local treatment during sinoscopy also improved the mucosal appearance in 8 patients.