The purpose of this study was to determine the relationship between serum leptin levels and body composition and to evaluate the variables related to disease in children and adolescents with type 1 diabetes. We studied 49 diabetic patients aged 6-16 years (age: 11.2+/-2.9 years, M/F: 26/23), and 37 healthy controls. Body composition was determined by dual-energy X-ray absorptiometry. Serum leptin, glycated hemoglobin (HbA1c), free thyroxin, thyrotropin, testosterone and estradiol levels were measured in patients and controls. We did not observe significant difference in serum leptin levels between patients and controls. Girls had significantly higher serum leptin levels than boys in both patient and control groups. Serum leptin levels did not correlate significantly with HbA1c, disease duration or daily insulin dose but, correlated positively with body mass index (BMI) and fat mass (FM) in patients as in controls. Body composition in diabetic girls and boys was similar with respective controls. When analyzed by pubertal stage, BMI, lean body mass (LBM), FM, and total bone mineral density (BMD) were significantly higher in pubertal girls with type 1 diabetes compared to prepubertal ones. In pubertal boys with type 1 diabetes, LBM and FM were significantly higher than prepubertal ones. The results of the present study showed that neither serum leptin levels nor body composition was significantly altered in children and adolescents with type 1 diabetes managed with intensive insulin therapy.