The aim of this study was to estimate insulin resistance in newly diagnosed type 1 diabetic children and adolescents and to analyse the correlation between insulin secretion and impaired insulin action. 37 patients with type 1 diabetes mellitus aged 12.9 +/- 3 years were included in the study. Duration of diabetes was 6 months. Euglycemic-hyperinsulinemic clamp was performed to estimate insulin resistance. Glucose disposal rate was calculated as index M - mg/kg/min. Insulin secretion was measured by glucagon test. The serum level of cholesterol, HDL-Ch, triglycerides and HbA1 was examined. The height, weight, skinfold, waist and hip circumference were measured. Body mass index and waist/hip ratio were calculated. In children and adolescents with type1 diabetes mellitus insulin resistance of various degree was observed. The glucose disposal rate (M index) was 3.2 - 11.8 mg/kg/min., mean 7.08 +/- 2.5 mg/kg/min. The insulin resistance depended on patients' age (r= - 0.3, p<0.05,) and the stage of puberty. There was no difference in insulin secretion in insulin-resistant and insulin-sensitive subjects. The insulin resistance was related to BMI (r=-0.33; p=0.04), and with skinfold thickness (r=-0.59; p=0.001). In insulin-sensitive children the insulin dose was lower (0.45: 0.67; p<0.02). No influence of insulin resistance on metabolic control was observed. Insulin resistance is observed in newly diagnosed type 1 diabetic children and adolescents. No relationship between insulin secretion and impaired insulin action was found. Insulin resistance was greater during III Tanner stage of puberty and in obese children.