Received December 14, 2011 Revised December 24, 2011 Accepted December 26, 2011 Address for correspondence Won Chul Shin, MD Department of Neurology, College of Medicine, Kyung Hee University, 892 Dongnam-ro, Gangdong-gu, Seoul 134-727, Korea Tel: +82-2-440-6166 Fax: +82-2-440-7243 E-mail: shinwc@khu.ac.kr Exploding head syndrome is a rare nocturnal disorder that the patient experiences a loud sound. The events occur usually during a period of drowsiness preceding sleep. The polysomnography studies in exploding head syndrome are very rare. We report a case of exploding head syndrome that a total of 8 typical episodes were recorded in polysomnography. A 51 years old female was admitted due to nocturnal loud sound from 2 month ago. There was no headache and no history of sleep problems. During the polysomnography, the events recorded 8 times, 6 of the events occurred during waking time prior to sleep onset, 2 developed in N1 sleep. In our case, the events appear to arise from early drowsiness with predominant alpha rhythm, with interspersed theta activity. J Korean Sleep Res Soc 2011;8:45-47