An antrochoanal polyp is a solitary polypoid mass that arises from the maxillary sinus, and protrudes through the natural ostium into the middle meatus, and reaches the choana. The polyp does not differ histologically from an ordinary nasal polyp, which is composed of edematous, hyperplastic submucosal connective tissue stroma, and is relatively hypocellular, In this sequence of events, its computed tomographic(CT) findings are characteristic. We retrospectively analyzed CT studies of nine cases, all of which showed similar CT findings; a solitary, homogeneous, hypodense mass without bony destruction that extends from the maxillary sinus through the widened ostium into the choana.