Radionuclide cisternography has the ability to show the CSF dynamics and it can be used to differentiate thevarious forms of hydrocephalus. The following results are obtained. 1. RI cisternography has been used to differentiate 38 cases of communicating hydrocephalus and 13 cases of noncommunicating hydrocephalus. 2. Gradingsof communicating hydrocephalus according to Harwood-Nash classification show the zero case of grade 1,2 cases ofgrade 2,10 cases of grade 3 and 26 cases of grade 4. Among these, 8 cases of grade 3 and 4 show symptomimprovement after shunt operation. RI cisternography of noncommunicating hydrocephalus shows normal finding in 13cases, among them 1 cas shows multiple photon defects, 3. The shunt survey was done in 3 patients. The patentshunt function was demonstrated in 2 cases, but shunt malfunction was identified in 1 case. 4. 2 cases ofporencephalic cyst and 1 case of arachnoid cyst show accumulation of radioactivity at the cyst in delayed scan. In conclusion, RI cisternography is useful to differentiate communicating from noncommunicating hydrocephalus and toevaluate cerebral atrophic change and circulating disturbance of CSF, in combination with Brain CT. The degree ofCSF flow distrurbance evaluated by RI cisternography can be used to plan the treatment which require shuntoperation. RI cisternography can also be applicable to study the patency of shunt, arachnoid cyst, porencephalic cyst, and site of CSF leakage.