The anurysmal bone cyst is a uncommon, non neoplasic, solitary bone lesion recognized by distinct radiographic and histopathologic characteristics.It is described as a localized, quickly expandible benign tumor, wich can reach a considerable size. It is characterized by the replacement of bone by spongy fibro-osseus, localy destructive tissue and a multicystric lesion filled with blood. we present a case report of a female patient of 14 year old with a giant tumor (20 cm diameter) in the left maxilla. Operated with total resection of the tumor and good aesthetic and funtional result at 4 yaer follow up. This aneurysmal bone cyst of the maxilla is the most largest reported.