For the sinus surgery, especially intranasal ethmoidectomy, it is necessary to get the precise anatomic informations before operation. For this, endoscopic and computerized tomographic(CT) diagnoses are important. The usual methods of CT scanning are the axial and coronal sectioning. But those sections do not directly show the planes which are met during surgery. To get the images showing the planes which are met during surgery, we took the direct sagittal and semiaxial(forms the angle of -18° with the infraorbitomeatal plane) images. These images had shown the anatomy of ethmoid sinuses more clearly than usual axial and coronal sections. The three dimensional structure could be understood more easily. These sectioning method were thought to be one of the good methods to show the surgical anatomy of the paranasal sinuses.