The purpose of the present study was to compare the new criteria by the International Headache Society (IHS) with criteria for the definition of childhood migraine previously used. In particular, we considered the problem of the minimally acceptable headache duration in children. In a postal questionnaire, 36.5% of 3580 children 8-9 years old reported headache attacks. Ninety-five children (2.7%) fulfilled the IHS criteria. Three percent fulfilled the previously used migraine definition of Vahlquist. Some of the children in the latter group had considerably shorter headache attacks than those of the IHS patients, but otherwise their symptoms were very similar. When the IHS criterion of headache attack duration was lowered from a minimum of 2 h to 1 h, or omitted, the number of migraine patients increased from 95 to 114 and 127, respectively.