Most cases of sinusitis are the consequence of anatomical abnormalities within ostiomeatal unit or disturbed mucocilliary flow. This ostiomeatal unit is the first place to be contact with bacteria and allergic particles during inspiration, and obstructed easily with minute mucosal swelling due to anatomical narrowness. Therefore careful examination and accurate diagnosis of causative lesions in ostiomeatal unit is essential to treat sinus diseases effectively. Authors studied 50 patients(84 sides) who had visited our hospital with complaints of nasal symptoms and were diagnosed as paranasal sinusitis from Feb. to Jul. in 1990. We evaluated the anatomical lesions that affect ostiomeatal unit with endoscopy and CT scan. The results were as follows；1) Age and sex distribution showed most common in second and third decade. Twenty-seven were men and 23 were women. 2) Distribution of paranasal sinus disease was most common in maxillary sinus 78 sides and the other were ant. ethmoid sinus, post. ethmoid sinus, frontal sinus and sphenoid sinus in decreasing order. 3) In location of paranasal sinus disease, maxillary sinusitis combined with ant. ethmoid sinusitis was most common in 20 sides. 4) Anatomical variants that affect ostiomeatal unit were uncinate process lesions 51 sides, enlarged bulla ethmoidalis 49 sides, middle turbinate lesions 26 sides, nasoseptal deviation 18 sides, agger nasi cell 16 sides and Haller cell 6 sides.