AIM: To test the feasibility of a system for monitoring children's obesity and overweight based on data from electronic health records in the school health services. METHODS: Data on weight and height from electronic health records at school health services were collected for 10-year-olds in 2003-2004, 2004-2005 and 2005-2006. School health personnel extracted group-level data with a simple program installed on the computer containing the health records. Four Swedish municipalities were included in the study: Karlstad, Umeå, Västerås, and Ystad. RESULTS: The system achieved coverage of 92-96% of all children in 2005-2006. The overall prevalence rates were 4.2% (3.8-4.7%) obese and 22.0% (21.1-23.0%) overweight, including obesity. CONCLUSIONS: A system based on electronic health records from the school health services can successfully provide data. The system has practical, economical and ethical strengths.