Chronic sinusitis is caused by disturbance of natural drainage and ventilation of the sinuses, among these the anatomic variations involving the ostiomeatal unit(OMU) is prominent. This study was designed to determine what effects the anatomic variations that obstruct the anterior ethmoid and OMU have the etiology of frontal recess obstruction and frontal sinusitis. We compared 390 preoperative PNS CT of chronic sinusitis patients to 281 with frontal sinusitis involvement who underwent ESS from January 1992 to May 1994 under diagnosis of chronic sinusitis. Overall, anatomical varitions effecting the frontal sinus were seen in 462(94.1%) cases with pneumatized agger nasi cell, 314(64%) cases with large ethmoid bulla cell, 133(27.1%) cases with medially bent uncinate process. Uncinate process may bend laterally and insert into the lamina papyracea in 334(68%) cases. The presence of mucosal abnormality with the frontal sinus region was associated with a corresponding abnormality in the ipsilateral anterior ethmoid sinus in all cases.