In chronic paranasal sinusitis, the anterior ethmoid sinus is believed to be the key are in provoking sinusitis and known to be the first area to be involved. And its importance is widely known after the development of functional endoscopic sinus surgery(FESS). The paranasal sinus(PNS) CT scan is an prerequisite of FESS and by which the anterior ethmoid disease can be exactly seen. But still the plain X-ray is a first choice in diagnosing sinusitis. To evaluate the accuracy of palin X-ray in diagnosing anterior ethmoid disease, the 25 patients who had been suspected of having sinusitis were evaluated with both PNS CT scan and plain X-ray. The plain X-ray films and CT scan were interpreted by three radiologists and two otolayngologists independently. The results were as follows : 1) In case of anterior ethmoid sinusitis, the sensitivity and specificity of the plain X-ray for anterior ethmoid sinusitis were 73%, 65% respectively. The sensitivity and specificity of plain X-ray for infundibular disease in anterior ethmoid sinusitis were 66%, 68%, respectively. 2) In the case of early infundibular disease, the most limited of obstructive inflammatory patterm, the sensitivity of plain radiograph varied from 18% to 73%. Therefore the reliability is very low. Above results suggest the plain radiographs are inadequate for evaluation of anterior ethmoid sinusitis, especially early infundibular disease. CT scan can provide specific diagnosis and display the underlying causes of sinusitis in patterns with anterior ethmoid sinusitis.