The author is reporting 4 cases of postoperative cheek cyst, treated in Soo-Do Medical College Hospital, during the past one and a half year. In these 4 cases, the duration from the time of previous radical antrum operation to the time of the onset of these cyst symptoms were 20 years in three cases and 13 years in one case. The cysts were seroceles in two cases and pyoceles in another two cases. These cases were treated completely by means of the Caldwell-Luc's radical antrum operation procedure. The author also reviewed the literatures and put emphasis on the preventive measures of this late complication of the radical antrum operation, quoting the articles written previously by Dr. Gill R. Kim.