The purpose of this study is to delineate the nature of the occurrence of benign mucosal cysts in a Seoul National University Hospital population by use of orthopantomographs and to help their differentiation from more serious antral diseases. 2143 orthopantomographs were scrutinized for evidence of benign mucosal cyst, and following results were obtained from the study. 1. An incidence of 3.3% was found. 2. The lesions were found in all age groups and their mean age was 35.2 years of age. 3. The incidence was higer in males as compared to females. 4. The majority of lesions were single, unilateral and situated on the floor of the antrum. 5. The size of the lesions varied. from 7.2㎜ × 16.0㎜ to 40.0㎜ × 49.5㎜ and the mean size was 22.9㎜ × 26.5㎜. 6. There was no significant relationship between the occurrence of benign mucosal cyst and odontogenic factors.