Purpose: In order to classify the involving patterns of maxillary sinus aspergillosis on CT that will be animportant guidance for functional endoscopic sinus surgery(FESS) and to evaluate CT findings of each pattern.Materials and Methods: We reviewed CT findings of 37 cases of maxillary sinus aspergillosis which were confirmedpathologically. These were classified into three patterns according to the location:the maxillary pattern( I ),the infundibular pattern(II), and combined pattern(III). All cases were correlated with FESS findings. We alsoevaluated CT density, presence of contrast enahncement and calcifications, and surrounding bony changes of eachpattern. Result: The combined pattern was most commonly seen in 24 of 37 cases(64.9%). The maxillary pattern wasidentified in 8(21.6%), with 5(13.5%)cases demonstrating the infundibular patttern. These patterns were consistentwith FESS findings. Calcifications were seen in 28 cases(75.7%). 31 cases(83.8%) revealed hypodensity and 16casesamong them showed peripheral enhancement. Central high density with peripheral low density rim was showed in25%(2/8) of the maxillary pattern and 12.5%(3/24) of combined patttern. Surrounding bony changes were noted mainlyin infundibular pattern and combined pattern. Erosion of uncinate process showed all cases of both patterns.Erosion or elevation of ethmomaxillary plate was seen in 3 of 5 cases of infundibular pattern and all cases of thecombined pattern. Conclusion: CT fidnings of maxillary sinus aspergillosis can be classified into 3 patternsaccording to their distribution. These classification could be helpful for planning FESS approach. Calcificationsare the most characteristic findings of maxillary sinus aspergllosis whereas CT desnity or enhancement pattern donot contribute to diagnosis.