Abstract It is postulated that Thornwaldt's cysts result from the failure of regression of notochordal tissue in the posterior nasopharyngeal area. The cysts may become infected and cause symptoms of nasopharyngeal drainage, occipital headaches and unpleasant taste in the mouth. The physical findings of a mid-line pouch in the postero-superior angle of the nasopharynx correlate well with the radiographic appearance of a soft tissue mass projecting into the radiolucent nasopharyngeal air space. The differential radiographic features are superior location, absence of surrounding soft tissue reaction and lack of osseous involvement. The radiographic appearance, although not specific, is felt to be characteristic.