BACKGROUND Child body mass index (BMI) is an internationally accepted indicator to assess child health status. International BMI reference curves are available but their suitability for Iranian children in not known. OBJECTIVE This study aimed to produce BMI-for-age growth curves for northern Iranian schoolchildren aged 7-11 years and compare them with the World Health Organization (WHO 2006) and Centers for Disease Control and Prevention (CDC 2000) reference curves. METHODS Stratified multistage cluster sampling was used to select schoolchildren from urban and rural areas of Babol. Height and weight were measured and BMI calculated. Smoothed BMI-for-age growth curves were constructed for both sexes and compared with the WHO and CDC reference curves. RESULTS A total of 4 083 children aged 7-11 years were included; 48.8% were boys and 56.7% were urban residents The major significant differences between the Iranian curves in this study and the CDC2000 and WHO 2006 growth charts were in the upper centiles. The 5th centile is close to the 5th centiles of the reference curves. CONCLUSIONS BMI centiles for 7-11 years schoolchildren in Babol differed significantly from the international growth reference curves. Therefore, local and population-specific BMI curves should be developed to assess physical growth of children.