A 73-year-old man (164cm height 51 kg body weight) with a history of Parkinson's disease and dementia was scheduled for a cervical lymph node biopsy under general anesthesia. We induced anesthesia with thiamylal and fentanyl, and maintained with sevoflurane and remifentanil without any incident. The patient did not emerge from anesthesia after the surgery. He developed coma and did not respond to painful stimuli. However, his breathing was spontaneous with stable hemodynamics. Although naloxone was given, he was still comatose. His clinical neurological findings showed no organic abnormalities. Forty minutes after the surgery, he suddenly woke up and followed instructions. We learned that previously he had been diagnosed with dementia with Lewy bodies.