Medication-overuse headache(MOH) is a clinically important entity and it is well documented that the regular use of acute symptomatic medication by patients with migraine or tension type headache increases the risk of aggravation of the primary headache disorders. MOH is one of the most common causes of chronic refractory headache. The pathophysiological mechanism of MOH is still unclear. But as in most of the headache entities, several different aspects, such as genetic background, peripheral and central nervous system interaction, specific psychotropic effects, appear to play key roles. Management of MOH is a difficult problem. The education for patients with MOH is very important.