These experimental studies of skull fractures in the temporal region were carried out in co-operation the Faculty of Engineering and the Department of Neurosurgery of Tokyo University. 15 dry human skulls were statically compressed in the bitemporal direction. The results of our experiments are as follows: 1) The forces necessary to produce the first fracture (seperations of the parietotemporal suture) are between 135 kg and 385 kg. (average; 258 kg) 2) The forces necessary to produce the second fractures (true fractures) are between 195 kg and 550 kg. (average; 356.3 kg) 3) The decreases of the inner diameters of skulls from pre-examination to the first fracture are between 0.65 mm and 1.85 mm. 4) The decreases of the inner diameters of skulls from pre-examination to the second fracture are between 1.56 mm and 4.5 mm. 5) The forces necessary to reduce the inner diameters of skulls by 1 milimeter are between 85 kg/mm and 380 kg/mm. (average; 221 kg/mm) The forces necessary to produce a fracture in the temporal region are much less than the forces necessary to do so in the frontal region. In deforming the skull, it is necessary to apply much greater force to the frontal region than it is to the temporal region. The relation between the skull's age and the minimal force to produce the skull fracture is not clear from the results of these experiments. The weights of the skulls were directly related to the minimal force necessary to produce skull fractures. Breaks in the inner table preceded those of the outer table when linear fractures occurred over the compressed area. when depressed fractures formed in the same area, the outer table was broken before the inner table. When the linear fractures formed far from the same area, the outer table was broken before the inner table. From our investigations on sports injuries, those players who died after being hit by golf balls or baseballs showed the same clinical courses as in typical extradural hematoma. Plain X-ray examinations of those fataly injured players did not reveal any skull fractures. Plain X-ray examinations of fractured skulls often failed to reveal the lesion unless the bone fracture was widely separated. On the basis of the above results, it would appear that routine skull films using either anterior-posterior or lateral projections are inadequate for the diagnosis of skull fractures. We have had good results in the examination of skull fracture by using the stereo X-ray method.