Two hundred ninety five consecutive brain CT examinations of asymptomatic adults were studied prospectively for detection of nontumoral paranasal sinus abnormalities. CT alterations were found in 104 cases (35.3%), localized to the ethmoid cells in 83 cases, the maxillary sinuses in 56 cases, the sphenoid sinuses in 19 cases, and the frontal sinuses in 18 cases. The relationships between ethmoid cells disease and alterations of the large paranasal cavities are analysed, and the association with previous sinusitis or rhinitis is evaluated. Frontal sinus disease is associated in more than two-thirds of the cases with pathologic meatic and/or unciform ethmoid cells, but such an association could not be demonstrated for the other cavities.