The CT studies of 198 consecutive patients with chronic sinusitis were reviewed retrospectively. CT was normal in 47 patients (23.7%). In 151 patients one or many cavities showed abnormalities. In 69 cases (34.9%), the lesions affected one or two sinuses, in 35 cases (17.7%) three to six cavities were abnormal, whereas in 47 cases (23.7%), more than six cavities were abnormal. In 87 cases (57.6%), lesions were observed both in large cavities and ethmoid cells, whereas they were selectively localized in large cavities in 55 cases (36.4%), or in ethmoid cells in 9 cases (6%). Abnormalities were observed in the maxillary sinus in 137 patients (69.2%), in the ethmoid in 96 patients (48.5%), in the frontal sinus in 51 patients (25.8%), and in the sphenoid sinus in 28 patients (14.1%). The most frequent abnormality was hypertrophic mucosa, which was visible in 275 cavities. These results were compared with date of the literature.