Spontaneous intracranial hypotension (SIH) is characterized by severe postural headache and low cerebrospinal fluid (CSF) pressure. Radionuclide cisternography (RC) is of some value in diagnosing CSF leakage causing SIH. However, the sensitivity of RC is too low to demonstrate the site of leakage. In these cases, the early appearance of the radioactivity in the urinary bladder has also been used as an indirect finding in the diagnosis of SIH. The aim of this study was to evaluate the diagnostic reliability of early urinary bladder activity as an indirect sign of SIH. We investigated early bladder activity in 21 patients with suspicion of normal pressure hydrocephalus. Of the 21 subjects, 13 (62%) showed early bladder activity. We demonstrated that early bladder activity is observed in patients without CSF leakage such as normal pressure hydrocephalus. Therefore, this indirect finding of RC is not a reliable finding in diagnosing SIH.