A new method of computerized tomographic scanning, surgical plane computerized tomography(CT), was designed for the preoperative evaluation of ostiomeatal unit(OMU) diseases. The images were taken by angulating the gantry at intervals of 5 degrees in the range of 40 degrees, with the subnasale used as a center of the circle. Distances between the mid-point of the posterior edge of the nostril(the point of reference) and the important anatomical structures were also measured by CT. Almost all parts of OMU were scanned within this 40 degrees. This technique is thought to be a valuable tool for the presurgical evaluation of OMU diseases, especially in cases of chronic paranasal sinusitis with diffuse polyposis and in cases where the usual anatomic landmarks have been distorted or removed by previous surgery. Furthermore it may be more helpful if it is accompanied with coronal and axial plane CT.