INTRODUCTION: To summarise key findings from research performed using data from the Copenhagen School Health Records Register over the last 30 years with a main focus on obesity-related research. The register contains computerised anthropometric information on 372,636 schoolchildren from the capital city of Denmark. Additional information on the cohort members has been obtained via linkages with population studies and national registers. RESEARCH TOPICS: Studies using data from the register have made important contributions in the areas of the aetiology of obesity, the development of the obesity epidemic, and the long-term health consequences of birth weight as well as body size and growth in childhood. CONCLUSION: Research using this unique register is ongoing, and its contributions to the study of obesity as well as other topics will continue for years to come.