Objective: Adiponectin plays an important role in pathophysiology of obesity, type 2 diabetes and cardiovascular disease. The aim of this study was to determine adiponectin concentrations in children and adolescents with type 1 diabetes in a longitudinal manner and to study the impact of age, gender, body mass index (BMI) and metabolic control. Research design and methods: In this study, 88 children and adolescents with type 1 diabetes were followed longitudinally. At baseline and during follow-up, serum levels of adiponectin were measured by enzyme-linked immunoassay and correlated with clinical data, HbA1c and lipids. Healthy children (nZ259) were chosen as a control group. Results: Serum adiponectin levels were significantly higher in children with type 1 diabetes compared with healthy children (13.1 vs 9.1 mg/ml at baseline, P!0.001). Adiponectin concentrations inversely correlated with BMI S.D.s (P!0.001). No significant difference of adiponectin levels regarding gender, diabetes duration or HbA1c was seen. Adiponectin concentrations decreased in males with type 1 diabetes during puberty (PZ0.03) while there was no significant change in females. In a subgroup of patients with new onset type 1 diabetes, adiponectin concentrations were not different from adiponectin levels in control subjects but increased during follow-up (PZ0.007). Stepwise multiple regression analysis showed that most important predictors of adiponectin levels in type 1 diabetes at the end of the study were adiponectin concentration at baseline (bZ0.574, P!0.001) and BMI S.D.s (bZK0.302, PZ0.001, r 2 Z0.56). Conclusions: Children and adolescents with type 1 diabetes have BMI-dependent elevated serum concentrations of adiponectin compared with healthy children.European Journal of Endocrinology 157 481-489