A 38-year-old man with past history of head injury at the age of 16 years was admitted to our hospital in April, 2000 because of bacterial meningitis. At the end of March 2000, he experienced massive cerebrospinal fluid (CSF) rhinorrhea when he rested in bed, and subsequently he developed high-grade fever, headache, and nuchal stiffness in 2 weeks. His symptoms and signs improved with the antibiotic therapy alone. He had no recurrence of meningitis since then. A defect of his right skull base was clarified by 3D-CT, and multiplanar reconstruction (MPR)-CT. MRI brain scan showed the dislocation of the right frontal lobe into the ipsilateral anterior ethmoidal sinus. The diagnosis of CSF rhinorrhea and bacterial meningoencephalitis were made according to his clinical manifestations and neuroradiological studies including 3D-CT, MPR-CT and MRI brain scans. These imaging modalities, which described his head anatomy precisely, helped us to clarify the cause of his illness. When CSF rhinorrhea is present, it is important to take detailed past history of head trauma, even if the event occurred more than 20 years previously.