Radionuclide cisternography is generally considered to be a safe procedure without significant neurological complications. However, in this report we present a patient who developed conus medullaris syndrome following radionuclide cisternography. A 46-year-old woman underwent lumbar puncture followed by radionuclide cisternography with the diagnosis of hydrocephalus. After the cisternography, she developed voiding difficulty with perineal sensory loss. Lumbar MRI revealed a high signal intensity lesion on T2-weighted images at the level of conus medullaris. Considering its clinical course and MRI findings, a spinal cord infarction is highly suggested as a cause of the conus medullaris lesion in this patient.