Chronic migraine and transformed migraine are conditions with a progression from episodic to chronic headache, a disabling stage. During attack, cutaneous allodynia frequently occurs: it reflects sensitisation of the central neurons of the trigeminovascular system. Early triptan therapy (prior to the development of central sensitisation) may protect from the chronicisation of migraine. In addition, early recognition of non-headache changes in neurologic function between episodes of headache offers a sensitive indicator of headache transformation. Attack frequency is the stronger predictor for migraine progression: prophylactic agents could be administered to patients with a high number of attacks. Medication overuse is the most important iatrogenic risk factor for the acceleration of disease and it must be prevented; other important risk factors are female sex, obesity and stressful life events.