Sinoscopy as an endoscopic investigative method of examining the maxillary sinus offers the advantage of a direct local interpretation in contrast to the usual indirect methods. The beginning of sinoscopy dates back to Hirschmann (1903) and Spielberg (1922). During the last 20 years, this method has been reintroduced and refined. In spite of a large number of articles about sinoscopy from Europe, there have been no articles about sinoscopy from Korea. In the present study, 182 maxillary sinuses were examined by sinoscopy and PNS Xpray for diagnostic reasons. The failure rate in sinoscopy was 3.8% and the rate of incomplete sinoscopy was inferior to X-ray. The detection rate of antral secretion by sinoscopy was higher than by Xpray. In the bacteriological study of antral secretions the percentage of no-growth specimens was 75.7%. In all approximately ten strains of bacteria were isolated from the secretions. Among them, streptococcus was the most common organism found. Therapeutic sinoscopy was performed in 16 patients who suffered from subacute or chronic maxillary sinusitis. In 8 of these patients, local treatment during therapeutic sinoscopy improved the mucosal appearance.