Roentgenological studies of the pneumatization and cell structures of the temporal bone among 319 cases of chronic otitis media have yielded following observations ; 1) Among the unilaterally affected cases the pneumatization of the unaffected side was below that of the normal ear; there was the higher incidence of the underdeveloped type than that of the normal ear, and therefore the unaffected ear is not always considered normal. 2) The pneumatization of the affected temporal bone in chronic otitis media revealed the underdeveloped type in 92.15% of the cases presenting a severe sclerosis. 3) While in normal person the pneumatization of the both ears were usually of same grade, in the unilaterally affected cases only the affected ear presented severe sclerosis and few of these had pneumatization of same grade. In bilaterally affected cases both side presented severe sclerosis and a higher percentage of these cases had same grade of pneumatization than that of the normal persons. 4) The cell structures of the unaffected side in unilaterally affected cases were more frequently irregular than those of the normal persons. In the affected side sclerosis was so severe that it was usually impossible to differentiate all structures. 5) In unilaterally affected cases the affected side revealed relative increase in small-sized cells, less irregular cell arrangement, and relative increase in number of the thick-walled cells. Severe sclerosis in these cases made it impossible to differentiate cell structures. In view of the above findings it is thought that the influence of chronic otitis media upon the pneumatization of the temporal bone is considerable. 6) In the unilaterally affected cases an analytical study on the unaffected side was made according the findings of the ear drum either normal or abnormal. In the normal group the percentage of the well-developed type was higher than that of the unaffected side as a whole, but lower than that of the normal person mentioned in Part 1. In the abnormal group the percentage of the well-developed type on the unaffected side was higher than that on type affected side, but was much lower than either that of the normal person or that of the unaffected side as a whole. Generally, an abnormal finding in the ear drum sugests a history of an inflammation or irritation of some sort in the middle ear, and it is conceivable that such an inflammation or irritation may hinder the development of the pneumatization. 7) In the affected ear, generally, the more chronic and the more grave the clinical course, the higher incidence of the highly underdeveloped type. It is suggesting that the pneumatization is influenced by the clinical course and the severity of chronic otitis media. 8) In view of the above observations, it is concluded that the sclerosis of the pneumatization of the temporal bone is influenced by chronic otitis media as well as by congenital factors.