the aim of this study was to review systematically the prevalence of headache and migraine in children and adolescents and to study the influence of sex, age, and region of residence on the epidemiology. we systematically searched the literature in electronic databases to cover the period between 1 January 1990 and 31 December 2007. We assessed and included population-based studies on epidemiology of headache and migraine in children and adolescents if they fulfilled the following criteria: (1) reporting on unselected childhood population; (2) reliable methods of data collection using a questionnaire or face-to-face interviews; (3) using the International Headache Society's (IHS) criteria (1988 or 2004) for the diagnosis of migraine; and (4) provision of sufficient and explicit data for analysis. We used Excel, Stata, and Confidence Interval Analysis software. we identified and analysed 50 population-based studies reporting the prevalence of headache and/or migraine in children and adolescents (<20y). The estimated prevalence of headache over periods between 1 month and lifetime in children and adolescents is 58.4% (95% confidence interval [CI] 58.1-58.8). Females are more likely to have headache than males (odds ratio [OR] 1.53, 95% CI 1.48-1.6). The prevalence of migraine over periods between 6 months and lifetime is 7.7% (95% CI 7.6-7.8). Females are more likely than males to have migraine (OR 1.67, 95% CI 1.60-1.75). Regional differences in prevalence of migraine, though statistically significant, may not be of clinical significance. The change in the IHS's criteria for the diagnosis of migraine was not associated with any significant change in the prevalence of migraine. this study confirms the global high prevalence of headache and migraine in children and adolescents. Sex, age, and regional differences are evident.