This report was to show the radiographic appearances of the fungus ball in a paranasal sinus and to emphasize the scan area of cone beam computed tomography (CBCT) to detect the calcification in the paranasal sinus. A seventyfour-year-old woman visited our department for the implant rehabilitation at both maxillary posterior edentulous region. Pre-operative radiographic examinations including the panoramic, CBCT, and multidector CT images were taken. An opacification in the right maxillary sinus was observed on the multiplanar image of CBCT, however the pre-determined scan area of CBCT in this report hardly showed the calcifications at the central portion of the maxillary sinus. The opacification in the maxillary sinus could be misdiagnosed as chronic maxillary sinusitis if the calcification of fungus ball was not simultaneously detected. The scan area of pre-operative CBCT needs to be enough to scan the paranasal sinus from top to bottom.