In order to study on the pneumatization of the temporal bone, 114 cases of healthy young adults were chosen and roentgenograms of temporal bone on Law's and Stenvers' view were taken. Surveys were made statistically on the distribution of types of pneumatization(classified in 6 grades) and cell structures. Following results were obtained. 1) The over-all distribution of types of pneumatization is 89.03±2.06% for the well-developed type and 10.96±2.06% for the underdeveloped type. Attention must be directed to the fact that the well-developed cases were seen in high percentage and that not a single case of the highly underdeveloped grade could be seen in this study. 2) When the pneumatization of the right and left temporal bones were compared, 90.35±2.76% of the cases revealed same types and 59.64±4.59% of the cases revealed same grades between the two. Among those having same types on both sides, 91.17±3.43% of cases belonged to the well-developed type. 3) The cell structures of the pneumatization of the temporal bone were regular in 60.08±3.24% and irregular in 39.91±3.24%. 4) When the cell structures of the right and left temporal bones were compared 78.06±3.87% of cases were of same structures. 5) Analytical study of the components of the cell structures revealed the presence of the medium-sized cells, the presence of medium degree in cell arrangement, and the presence of the thin cell wall in high percentages respectively.