There are three types of swelling of the neck which develop during peroral endoscopy. One is the swelling called Compton's pouch, which occurres at the subman.dibular region. This swelling is presumed to be due to air distention of blind Branchial cleft remnants. Gagging and retching by the patient during endoscopy are thought to force air blow into the remaining pouches of Branchial clefts. Compton's pouch is clinically insignificant other than demonstration of the presence of these vestigial remnants. This swelling is not so firm and can easily be sqeezed flat, or left alone, it deflates spontaneously in about half or one hour. This is very rare complication and we have experienced only a few times for the last several years. Second type is produced by the distended or displaced submaxillary salivary gland. This occurres almost at the same place as Compton's pounhh and is also symptomless, but this type of swelling is relatively firm and cannot be deflated by pressure. This may disappear spontaneously in 2 to 12 hours. This is also rare, but we experienced two caces of swelling thought to be of this type. The swellings in both two cases occurred during esophagoscopy. In one of them it occurred two times. The exact incidence is probably 0.05%, since we experienced three times in about 6, 000 esophagoscopic examinations. The last type is the swelling which is seen at the preauricular area and is thought to be the swelling of the paroticl gland. This may be producedd in the same way as the submaxillary salivary gland swelling judging from it's nature. This is also rare, occurred only a few times seen in one case in the course of about 50, 000 peroral endoscopies performed by the authors.