We report a patient who developed bacterial meningitis after radiofrequency thermocoagulation of the Gasserian ganglion. A 50-year-old man underwent this procedure for treatment of cancer pain of the mandible. The pain subsequently decreased; however, headache and elevation of the body temperature up to 39°C occurred the first night following the procedure. The patient showed no apparent sign of meningeal irritation. However, a cerebrospinal fluid examination four days after the procedure revealed pleocytosis, elevated protein level, and decreased glucose level, suggesting bacterial meningitis. Antibiotics were changed to panipenem/betamipron 4 g/day and vancomycin 2 g/day. The headache and pyrexia disappeared eight days after the procedure, and there were no apparent neurological deficits.