PURPOSE: To determine whether the wall thickening of the maxillary sinus is a characteristic finding in aspergillosis. MATERIALS AND METHODS: In 103 patients, including 26 with aspergillosis, 21 with inverted papilloma (IP), and 56 with unilateral chronic sinusitis, the thickness of the maxillary sinus wall was determined by CT scanning. All cases were proven pathologically, and patients with a history of previous surgery or bone destruction were excluded. Two neuroradiologists retrospectively reviewed the CT scans using bone window settings for sinus wall hyperostosis and the presence of intrasinus calcification. Thickening of the maxillary sinus wall was assessed visually in a semiquantitative manner, and graded as 'none'(absence of thickening), 'mild'(thickening of up to 1.5 times), or moderate to severe(over 1.5 times thicker than normal contralateral sinus wall at its thickest point). RESULTS: Moderate to severe wall thickening was found only in patients with aspergillosis (21/26, 80.8%). Mild wall thickening was seen in two patients with aspergillosis (2/26, 7.7%), in 12 of 21 with IP (57.1%), and in 5 of 56 with chronic maxillary sinusitis (8.9%). Most cases of chronic maxillary sinusits (51/56, 91.1%), 9/21 IP cases (42.9%), and 3/26 cases of aspergillosis (11.5%) showed no thickening of the maxillary sinus wall. Calcifications were found in 18 patients with aspergillosis (69.2%), in no patient with IP (0%), and in one with chronic maxillary sinusitis (1.8%). CONCLUSION: We suggest that 'moderate to severe' wall thickening of the maxillary sinus is the characteristic finding of aspergillosis. Although various sinonasal diseases can cause bone change, CT findings of hyperostosis of the maxillary sinus and intrasinus calcification are very helpful in differentiating fungal sinusitis from other types of chronic inflammatory lesions.