Objectives-To determine the prevalence rates of the various causes of severe headache in schoolchildren, with special emphasis on migraine and its impact on school attendance.Design-Population based study in two stages, comprising an initial screening questionnaire followed by clinical interviews and examination of children with symptoms and a control group of asymptomatic children matched for age and sex.Setting-67 primary and secondary schools in the city ofAberdeen.Subjects-2165 children, representing a random sample of 10/o of schoolchildren in Aberdeen aged 5-15 years.Main outcome measures-(a) the prevalence of migraine (International Headache Society criteria) and of other types of headache; (b) the impact of migraine on school attendance.Results-The estimated prevalence rates of migraine and tension headache were 10X60%o (95% confidence interval 9 1 to 12.3) and 0 9%'/o (0*5 to 1.5) respectively. The estimated prevalence rates for migraine without aura and migraine with aura were 7-80/ (95% confidence interval 6*5 to 9.3) and 2-80/ (2-0 to 3.8) respectively. In addition, 10 children (0 70/6) had headaches which, though lasting less than two hours, also fulfilled the International Headache Society criteria for migraine, 14 (0 9%/) had tension headaches, and 20 (13%/) had non-specific recurrent headache. The prevalence of migraine increased with age, with male preponderance in children under 12 and female preponderance thereafter. Children with migraine lost a mean of [7][8]