A 13-month-old girl developed opsoclonus-myoclonus syndrome in association with neuroblastoma. She showed irritability, hyperhidrosis and a bad temper. Serum and urinary vanilmandelic acid, homovanilic acid and catecholamines were elevated at the same time. Chest CT demonstrated the presence of neuroblastoma in the paravertebral region. Cranial CT and MRI revealed no abnormal findings. Brainstem auditory-evoked potentials and short latency somatosensory evoked potentials were normal, whereas blink reflex showed long duration and high amplitude of late components (R2 and R2') indicating hyperexcitability of the interneurons in the lower brainstem. These findings improved gradually as opsoclonus disappeared. Her neurologic symptoms resolved completely within 2 years after the resection of the tumor. The hyperexcitability of the blink reflex may indicate the hyperactivity of the neurons in the brainstem reticular formation responsible for the abnormal saccadic eye movements (opsoclonus), which could be caused by the oversecretion of dopamine or by the supersensitivity of dopaminergic receptors.