The posterior fossa, which contains about one fourth of the intracranial contents, is the site of known about two thirds of pediatric intracranial tumors. In about such tumors are less common and the prognosis may bevery poor. However, it is important to recognize the earliest symptoms because of the relatively high ease rate of operable management and the possibility for a high cure rate in some cases. A series of 51 pathologically verified posterior fossa tumors seen at the Department of Neurosurgery, Yonsei University, Severance Hospital over several years were studied. These tumors were explored surgically, and the diagnosis being made through histological examination. The cases were reviewed as to history, development and progression of the neurological features, laboratory findings, roentgenograms, differential diagnosis, operative methods and findings, and pathology. The authors emphasized some interesting points which are illustrated as follows; 1. Among 51 cases of posterior fossa tumors, 25 cases of acoustic neuroma, 9 cases of astrocytoma, 9 cases of medulloblastoma, 2 cases of ependymoma, 3 cases of pontine glioma and 3 cases of cysticercosis in the fourth ventricle were found, comprising 21 males and 30 females. 2. The 25 operated cases of acoustic neuroma were between the age of 20 and 60. Eighteen cases(69.2%) of the remaining posterior fossa tumors were below the age of 15. 3. The author was able to make the correct plain film diagnosis of acoustic neuroma in 13 cases(51%) of 25 cases. The prominent angiographic and ventriculographic finding of posterior fossa tumors was ventricular dilatation. 4. Vntriculogram was very important in the diagnosis of the fourth ventricle tumors. The Conray ventriculogram had the special benefit in accurately outlining and demonstrating the invasive pattern of fourth ventricle tumors. The Conray showed C.S.F. flow in malignant and other large tumors in the fourth ventricle better than was shown by previous pneumo-ventriculograms. 5. The Electroencephalogram showed an abnormal pattern in 62.2 per cent of 29 posterior fossa tumors.