In a retrospective study 170 computed tomographies recorded in patients with chronic sinus disease were evaluated. The extent of sinus disease and the involvement of the different paranasal sinuses were well seen. Up to now 50 patients have undergone surgical treatment. The coincidence of the preoperative CT with the intraoperative findings was about 90%. Anatomic particularities of the paranasal sinus in an individual patient may predispose to recurrent sinusitis or mean there is an increased risk of intraoperative complications. The main risk factors are a far lateral location of the posterior ethmoid cells (28.8%), a much lower position of the cribriform plate in comparison to the ethmoid roof (11.8%), and extensive lateral aeration of the sphenoidal sinus (1.2%). All patients should undergo CT scanning in coronal and axial planes prior to endonasal sinus surgery. This gives a guide for detection of inflammatory lesions and anatomic variations or anomalies, thus making it possible to prevent intraoperative complications.