Endoscopic endonasal surgery was performed on 64 patients (69 sides) with postoperative maxillary cyst. We marsupialized the cyst in the inferior and/or middle meatus to enlarge it as much as possible. To facilitate an easier approach to the cyst wall in the inferior nasal meatus, some patients underwent submucous resection of the inferior nasal concha or inferior turbinectomy. Thirty-eight patients (44 sides) were followed for more than six months after surgery and a wide opening was confirmed in 36 (81.8%) of the 44 sides. Whether we should utilize an endonasal approach or a Caldwell-Luc approach depends mainly on the location of the medial wall of the cyst. We classified the cysts into medial, anterolateral and posterolateral types. Drawing a line between the anterior end of the inferior turbinate and the base of the lateral pterygoid process, on the axial plane of CT at the mid level of the inferior meatus, is the first stop. A medial cyst extends toward the midline across this imaginary line. A lateral cyst is subdivided into anterolateral and posterolateral based on the position of the center of cyst. The endoscopic endonasal approach resulted in excellent outcomes in medial and posterolateral cysts, while this approach was not found to be suitable for anterolateral cysts.