A patient with hemiplegic migraine who was treated successfully with flunarizine is presented. A fifteen-year-old boy developed right hemiparesis during several migraine attacks. Regional cerebral blood flow (CBF) measurement using intravenously injected xenon 133 showed that the CBF was about 10-15% lower in left fronto-temporo-parietal regions than that on the contra-lateral side. After the treatment with flunarizine at a dose of 10 mg/day, he has been free of migraine attacks and hemiparesis disappeared. Regional CBF 1 month after treatment showed no decrease in any region of the brain. The findings indicate that flunarizine reversed the neurological deficits by increasing CBF by its vasodilating action.