Medication overuse headache (MOH) has developed into the third most common type of headache after tension-type headache and migraine. The prevalence of MOH is approximately 1% of the world's population and it shows an increasing trend as recent studies reveal a common involvement throughout the ages, even starting in childhood. All antiheadache drugs, such as triptans, analgesics, ergots and opioids, along with the common combination substances currently on the pharmacological market are capable of inducing MOH. New data on specific clinical features and mean critical monthly dosages and mean critical monthly intake frequencies are now available. The only effective treatment concept is consequent withdrawal therapy. Data of prospective studies on relapse rates and predictors of relapse after successful withdrawal therapy are presented.