It has been generally accepted that the scanning of the posterior fossa yield less accuracy in comparison with that of the supratentorial region. It seems that the difficulties are primarily attributable to the parotid gland, the overlying venous sinuses, and the heavy investment of the muscles with their rich vascular supply at the posterior fossa. These problems are compounded by poor patient positioning in the posterior view. We believe that the brain scanning of the posterior fossa is, however, nearly as successful as that of the supratentorial region, when the following procedures are carried out. We performed 99mTc-pertechnetate brain scanning 41 times and 169 Yb-DTPA cisternography 7 times on 25 posterior fossa tumors, from August 1970 to September, 1974. The diagnosis of these cases were confirmed by operation or autopsy. These include six neurinomas, six astrocytomas, three medulloblastomas, three hemangioblastomas, three metastatic tumors, one meningioma, one arteriovenous malformation, one osteochondroma and one microglioma.