In a 43-year-old woman, 1 ml of 5% fluorescein diluted with 10 ml of cerebrospinal fluid (CSF) was injected into the subarachnoid space at the L4-L5 level to evaluate nasal CSF leakage. After the injection, amnesia and grand mal seizure developed following a low-back pain spreading through the right leg. The patient was treated with antiedematous and anticonvulsant drugs. CSF drainage and vigorous hydration were performed. The patient recovered without sequelae. It was concluded that intrathecal fluorescein should be used with caution.