BACKGROUND: Recent experience in designing and running clinical trials on new medications for the prevention of migraine in children and adolescents highlighted the need for revision of the 1st edition of the International Headache Society Guidelines for clinical trials of preventive treatment of migraine in children and adolescents which were published in 2019. METHODS: The authors of the 1st edition of the guidelines formed an informal focus group with aims of appraising the performance of the guidelines, clarifying any ambiguity and providing improvements, where needed, based on personal experience and expert analysis. RESULTS: This review and the following update were able to address issues related to the classification of migraine, the duration of migraine attacks, the age groups of children and adolescents, the use of electronic diaries, the assessment of outcome measures, the need for an interim analysis and the issues related to placebo response. CONCLUSIONS: This update provides necessary clarifications of the guidelines in order to enable better design and running of future clinical trials for the preventive treatment of migraine in children and adolescents.