Unusual presentation of adenoid cystic carcinoma of the maxillary antrum. Adenoid cystic carcinoma (ACC) is a rare tumour which affects mainly the major and accessory salivary glands. It is an aggressive neoplasm characterized by early neural invasion and a high incidence of local recurrence and distant metastases, which may develop years after the initial resection. Surgery followed by radiotherapy seems to be the best treatment. Based on a well-illustrated case of extensive maxillary ACC involving the palate, orbit floor, and pterygo-palatine fossa, we discuss the prognosis and the importance of an early diagnosis of ACC.