The prevalence of overweight among Japanese children and adolescents has steadily increased during the last 20 years. Thus, we utilized the 1978-1981 data collected by the Japanese Ministry of International Trade and Industry to construct reference curves of body mass index (BMI) for contemporary Japanese children and adolescents. BMI reference values were derived using the LMS method as based on height and weight data from the cross-sectional national survey of Japanese children and adolescents conducted in 1978-1981 (14,012 boys and 13 781 girls, aged 1.5-18.5 years). The Japanese BMI reference curves were constructed for clinical use. The centile values at the upper end of the spectrum apparently differed in British, Dutch, Japanese, and US children and adolescents. In contrast, the centile values at the lower end of the spectrum nearly overlapped with each other in the four populations. Overweight is concentrated in a subgroup of children and does not occur across the entire population of British, Dutch, Japanese, and US children, indicating a subgroup of genetically and/or environmentally more susceptible children in each country.