The ethmoid sinus, like the other nasal sinuses, is extremely variable in anatomic characteristics. This honeycomb-like appearance of the ethmoid cells gives the impression of an entanglement as they are regarded as a labyrinth. A clear understanding of the normal anatomy and various characteristics of the ethmoid sinus of the Korean is reached only by examination of large series of specimens from cadavers. And it makes possible to diagnose and treat the nasal diseases properly. So far, there has been many studies on this aspect in the western countries and Japan, but in Korea we have still remained in unexplorative field. Therefore, the author examined 100 adult nasal cavities of 50 Korean cadavers in Yonsei University, College of Medicine. In this investigation, a study was carried to classify the ethmoid cells according to the location of drainage and determine the number of cells, status of shape and direction of osia, dimension and volume, extramural cellular extensions and relationship to the neighboring structures of the cells. And the following results were obtained. 1. Among 100 ethmoid sinuses, the cell count ranged from 3 to 14 in each sinus and in which 68 percent contained from 6 to 9 cells and 23 percent which was predominant, contained 6 cells. 2. The anterior group cells varied in number from 1 to 9 and in which 71 percent contained from 3 to 5 cells and 30 percent which was predominant, contained 4 cells. 3. The posterior group cells varied in number from 1 to 7 except only 1 sinus without any posterior group cell and in which 77 percent contained 2 to 4 cells and 42 percent which was predominant, contained 3 cells. 4. The dimensions of the ethmoid sinus were 3.59cm in anteroposterior length, 1.12cm in width and 1.68cm in height. The dimensions of the anterior group were 1.50cm in length. 0.89cm in width and 1.70cm in height and the posterior group were 2.09cm in length, 1.30cm in width and 1.81cm in height. 5. The volume of the anterior group was 2.48cm³, and the one of the posterior group was 3.05cm³. 6. Among the anterior cell group in detail, the frontal recess cell was presented in 45 percent and the number of the cells ranged from 1 to 3, and 38 sinuses and 84.4 percent of these contained single cell. The infundibular cell was presented in 98 percent, varied in number from none to 5 and the 83 sinuses and 84.7 percent of these contained 1 or 2 cells. The bullar recess cell was presented in 94 percent, varied in number from 1 to 5, and 74 sinuses and 78.7 percent of these contained 1 or 2 cells. 7. Among the posterior cell group in detail, the posterior cell draining into the superior meatus, was presented in 97 percent varied in number from 1 to 6, and 68 sinuses and 70.1 percent of these contained 2 or 3 cells. The postreme cell draining into the supreme meatus, was presented in 52 percent varied in number 1 or 2, and 41 sinuses and 78.8 percent of these contained single cell. 8. Among all of 100 sinuses, 59 percent had a supreme concha and 52 sinuses of these and 88.1 percent had a cell which drained into the supreme meatus. 9. Among the soecial cells, the middle concha cell was presented in 17 percent, and of these 16 percent was unicellular and 1 percent was bicellular. Of these, 15 percent drained into the superior meatus and 2 percent into the bullar recess. The agger cell was presented in 78 percent, and the uncinate cell in 3 percent. The bullar cell was presented in 95 percent, varied in number 1 to 3, and in which the single cell was 83 sinuse and 87.4 percent. And 79.8 percent of these cells drained into the bullar recess But remains of 20.2 percent drained into the infundibulum and the superior meatus. 10. The supraorbital cellular extension was presented in 43 percent of which 86.0 percent was unicellular origin and 14.0 percent was bicellular origin. And the cellullar extension to the frontal sinus was in 22 percent, extension to the minor wing of the sphenoid bone was in 29 percent, the extension to the sphenoid sinus was in 19 percent, the extension to the infraobital plate was in 12 percent and the extension to the maxillary sinus was in 1 percent. 11. The ostia of the cells varied in shape and size ; being commonly round or oval (80.0 percent), cresentric or spindle (14.4 percent) and non-specific shape (5.6 percent) in order. 12. The most ostia was advantageously faced and directed posteroinferiorly (48.5 percent), inferiorly (25.8 percent), anteroinferiorly (7.1%) and otherwise (10.8 percent), but rarely faced upward (7.8 percent). However, the openings upward were noticed considerably greater in bullar recess cells than others. 13. The occurance rate of the optic canal in the posterior ethmoid sinus was 52 percent, and the canals were projected into the sinus in 25 percent which are vulunerable during intranasal surgery. The length from the canal to the anterior nasal spine was 6.37cm and the angle from this length line to the nasal floor was 44.16°. 14. The length of the III lamella was 3.88cm, the angle to the nasal floor was 45.94° and the length from the upper attachment of the III lamella to the nasal floor was 4.94cm and the angle to the nasal floor was 59.09°.