The document discusses headache classification systems. It provides an overview of the old ad-hoc system and introduces the International Classification of Headache Disorders, 2nd edition (ICHD-2) which divides headaches into primary and secondary types. The ICD-9 code system is also discussed and revisions are proposed to bring it in line with current medical understanding and ICHD-2. New codes are suggested for cluster headaches, tension headaches, and other primary and secondary headache syndromes.