4. An interview investigation performed in 1955 in the form of a questionnaire covering 8,993 school children in Uppsala of ages 7 to 15 years was the basis of the frequency investigation of migraine in school children, described in Chnpter IV. This showed that migraine occurred in 4.096 of this material. For the age group 7-9 years the frequency figure was 2.5 yo, for boys 2.5%, for girls 2.4%; for the age group 10-12 years the frequency was 4.6%, for boys 3.9%, for girls 5.4%, which gave a probably significant (*) sex difference. The frequency for the age group 13-15 years was found to be 5.3%, for boys 4.0%, for girls 0.4 96, which also gave a probably significant (*) sex difference. The increase in frequency between the age group 7-9 years and that of 10-12 years was highly significant (***) for girls and probably significant (*) for boys. 5. The frequency figures preliminarily obtained from the questionnaires were adjusted, partly with regard to the sampling error and partly by the correction of the answers to the questionnaires.