Abstract: Objective: To analyze the CT manifestations of transtentorial herniation due to epidural hematoma,and to sudy the relationship between the volume of the hematoma and the degree of the herniation.Methods: Fifty-two cases of epidural hematoma due to cerebral hernia were examined by CT,with the scanning line perpendicular to the line from posterior elinoid process to the lowest point of the clivus(C-C line).Results: Transtentorial hernia was diagnosed by CT in 26 cases,presenting as an isodensity mass attached to the tenporal lobe and located medial to the tentorium in the ambient cistem.The hernias varied in size,being <3 mm(n=3),3-7 mm(n=6) or >7 mm(n=11).The volume of these differnt sized hernias was 31.3-34.5 ml,32.4-42.3 ml and 40.5-69.2 ml.Conclusions: By CT study with the scanning line perpendicular to C-C line,tentorial herniation due to epidural hemstoma can be accurately diagnosed.The volume of the hematoma is consistent with the degree of herniation.