Computed tomography (CT) is a very important diagnostic tool prior to endoscopic nasal or paranasal sinus surgery. However, it is frequently notice during endonsal surgery of the paranasal sinuses, that the intraoperative results do not completely agree with the radiological ones. The objective of the present study was to compare clinical and operative findings with those of CT investigations. We collected 200 cases treated during the past 2 years and studied their CT reports. Paranasal sinuses were separated into six regions, and the pathological changes due to sinusitis found by CT were classified into four groups. Altogether, we found a highly significant relationship between CT and intraoperative findings (r = 0.44; P < 0.0001), but differences were found in several regions. The highest correlation was found in the anterior ethmoid bone area (r = 0.98), posterior ethmoid bone area (r = 0.53), maxillary sinus (r = 0.36) and sphenoid sinus (r = 0.35). There was only a low agreement in the case of frontal sinus and recessus frontalis. Possible factors such as time between CT and operation or inflammation are discussed. While CT is the image modality of choice in evaluating patients with chronic paranasal sinusitis, agreement to intraoperative findings is not perfect. This should be taken into consideration when planning functional endoscopic sinus surgery.