To clarify the Pathogenesis and find the proper surgical treatment of oroantral fistula developed after tooth extraction, the medical records of 16 patients who underwent operations were analyzed retrospectively. On the bases of past history and paranasal sinus CT findings, we could classify the etiology into two group. The first group is ""odontogenic"" origin which is considered to occur from inflammation over dental root area including dentigerous cyst, remained tooth root necrosis after extraction, and periapical cyst. The other group is ""sinogenic"" origin due to preexisting maxillary sinus inflammation, for example, postoperative cheek cyst and incomplete Caldwell-Luc operation. The incidence of odontogenic and sinogenic origin was 67% and 33% respectively. All of the patient were successfully treated with buccal mucosal flap after Caldwell-Luc operation. However, it might be reasonable in pure odontogenic cases to perform minimal invasive treatment such as making nasoantral window to control sinusitis instead of radical maxillary sinus operation.