[The new IHS classification. Background and structure]

The diagnosis of headache is nowadays based on the classification criteria of the International Headache Society (IHS). This classification can be seen in a historical context with a very first version published by an ad-hoc-committee of the National Institute of Neurological Diseases and Blindness in the USA. In 1988 the first IHS version appeared, and this was revised in its current version in 2003. The classification is divided into primary (i.e., idiopathic) and secondary (i.e., symptomatic) headache and into cranial neuralgias and facial pain. The classification is based on the description of the headache features and thus a phenomenological rather than an etiological classification. Furthermore, not the patient as a subject but the headache as a clinical entity is classified. Therefore, some patients can have more than one headache diagnosis. In total, 14 different headache groups and more than 170 headache types are separated. The changes compared to the last classification (such as introduction of chronic migraine and of several new rare idiopathic headache disorders) and the perspectives for future classifications (e.g., problems of genetic classification) are discussed.