The present study was designed to determine the plasma level of orexin and its relationship with other metabolic and anthropometric markers in obese children. Forty-seven obese Japanese children, consisting of 31 boys and 16 girls, were enrolled in the study. Their ages were 10.4 ± 0.5 (mean ± s.e.m.) yr, and their percentage overweight was 42.9 ± 1.9%. Blood was drawn after an overnight fast. The age-matched control group consisted of 26 nonobese children, 13 boys and 13 girls. Plasma orexin-A concentration was higher in obese children (17.0 ± 0.4 pg/ml; p<0.001) than in the control children (13.5 ± 1.1 pg/ml). Similarly, plasma leptin concentration was higher in obese children (12.0 ± 1.0 ng/ml; p<0.001) than in the control children (5.2 ± 0.4 ng/ml). There was a highly significant positive correlation between the two parameters in the obese children (r=0.49, p<0.001). Plasma orexin-A level was correlated significantly with waist-to-hip ratio, while leptin level was correlated with percentage overweight, waist circumference and percentage body fat in the obese children. These results suggest that high plasma orexin-A level parallels the leptin level in obese children.