Radionuclide cisternography evaluates cerebrospinal fluid dynamics, while CT and magnetic resonance imaging provide better information about central nervous system anatomy. This article describes two cases of patients with hydrocephalus. Their radionuclide cysternography studies were initially felt to be normal. After correlation with CT scans, massively enlarged ventricles were discovered. Tracer activity had refluxed into the ventricles, simulating normal cerebrospinal fluid rise over the convexities. When radionuclide cisternography studies in patients with excessively enlarged ventriculars are interpreted, correlation with other anatomic imaging studies, such as CT and magnetic resonance imaging, is essential. A vertex view acquired during cisternography may also be helpful in correlation with transaxial plane images obtained by CT and magnetic resonance imaging.