Sleep is an important, but easily neglected issue in pain disorders, in both clinical and basic medical aspects. Many pain and headache disorders, such as fibromyalgia, small fiber neuropathy, cluster, migraine and hypnic headaches, are intimately related to disturbance in sleep physiology or circardian rhythm. Many pharmaceutical agents for pain, including tricyclic anti-depressants, also significantly affect sleep. Herein sleep medicine is reviewed for chronic pain management. Korean Journal of Headache 2(2):133-136, 2001