In 740 representative normal subjects a diagnostic headache interview and a neurological examination provided the necessary information to classify headache disorders according to the operational diagnostic criteria of the International Headache Society (IHS). Sixteen per cent (n = 119) had migraine, 78% (n = 578) tension-type headache. In migraineurs, pain was of a pulsating quality in 78%, severe in 85%, unilateral in 62%, and aggravated by routine physical activity in 96%. Tension-type headache was of a pressing quality in 78%, mild or moderate in 99%, bilateral in 90%, and 72% had no aggravation by physical activity. The accompanying symptoms of nausea, photo- and phonophobia occurred frequently and were usually moderate or severe in migraine subjects, and if present in subjects with tension-type headache, they were usually mild. Only two subjects had unclassifiable headache. The IHS Classification is thus exhaustive. The criteria may be improved by mandatory demands to the criterion of pain intensity leaving other features of pain as supportive for the diagnosis and by including graded severity of accompanying symptoms. A specific proposal is given.