Posterior fossa injury is a relatively infrequent in all craniocerebral injuries, which may be a rapidly fatal disease unless the diagnosis and prompt treatment are made. Delay in operation or failure to make the diagnosis early may result in death from medullary decompensation. An injury to the occipital region, followed by signs and symptoms of cerebellar or medullary nerve dysfunction, should cause one to suspect the existence of this lesion. It is well to remember that neither the surgically demonstrated presence of a supratentorial clot nor the roentgenological failure to demonstrate an occipital fracure excludes the presence of a mass lesion in the posterior fossa. Authors studied 104 cases of posterior fossa injury admitted at Department of Neurosurgery, Kyung Hee Medical Center from October 5 th, 1971 to August 30 th, 1974. The results were as follows: 1) The incidence of posterior fossa injury was 5.7% of all craniocerebral injuries. 2) The age incidence was greatest in the age group between 10 and 20. 27.9% of all cases were belonged in this group. 3) Common causes were traffic accident(82 cases:78.8%), falls from(14 cases:13.5%) and direct blow(6 cases:5.8%). 4) Male outnumbered female by almost 2 to 1. 5) Common symptoms were disturbance of consciousness(67 cases:64.4%), headache(43 cases:41.3%) and vomiting(24 cases:21.3%). 6) Scalp injuries were demonstrated in 95 cases and occipital, bone fracture in 58 cases under gross and radiological examination of posterior fossa. 7) Time interval between injury and operation was greatest at 3 to 6 hours. 8) In 30 cases of operation, massive cerebellar contusion was 13 cases, extradural hematoma was 7 cases and subdural hematoma was 2 cases and negative exploration was 6 cases. 9) The overall mortality rate was 25%.