The therapeutic effect of botulinum toxin in headache was observed coincidentally. The rationale for this new indication initially met with a great deal of scepticism, because the toxin's mechanism of action, cholinergic chemodenervation, does not fit the pathophysiological concept of migraine and other forms of headache. Meanwhile a fair number of studies have been published which indicate efficacy for botulinum toxin and recommend its use for the treatment of tension headache and migraine. According to the evidence-based medicine criteria, grade I evidence has been demonstrated. In addition the use of botulinum toxin for cluster-headache and secondary headache is discussed. Further large scale studies will be regarded to demonstrate the long-term efficacy.