A case of endosalpingiosis presented as a multilobular cyst on sonography. The tentative clinical diagnosis was an ovarian tumor; however, laparotomy revealed a degenerative cyst of the uterine myoma with a stalk connecting to the uterus. Histopathologically, it showed characteristics of endosalpingiosis. To our knowledge, such a multilobular cyst of endosalpingiosis originating solely from the uterine serosa has not been reported.