An insulin resistance syndrome (IRS) score was developed based on clinical risk factors in adults with childhood-onset type 1 diabetes in the Epidemiology of Diabetes Complications (EDC) Study and was validated using euglycemic-hyperinsulinemic clamp studies. Hypertension, waist-to-hip ratio (WHR), triglyceride and HDL cholesterol levels, family history of type 2 diabetes, and glycemic control were risk factors used to define the score. A score of 1 (lowest likelihood IRS) to 3 (highest likelihood IRS) was assigned for each risk factor. Eligible subjects (n = 24) were recruited from the EDC cohort based on tertile of IRS score. Subjects received an overnight insulin infusion to normalize glucose levels, then underwent a 3-h euglycemic-hyperinsulinemic (60 mU x m(-2) x min(-1)) clamp. Glucose disposal rate (GDR) was determined during the last 30 min of the clamp. The GDR differed significantly by IRS group (9.65 +/- 2.99, 8.02 +/- 1.39, and 5.68 +/- 2.16 mg x kg(-1) x min(-1), P < 0.01). The GDR was inversely correlated with the IRS score (r = -0.64, P < 0.01). Using linear regression, the combination of risk factors that yielded the highest adjusted r2 value (0.57, P < 0.001) were WHR, hypertension, and HbA1. This study found that clinical risk factors can be used to identify subjects with type 1 diabetes who are insulin resistant, and it provides validation of a score based on clinical factors to determine the extent of insulin resistance in type 1 diabetes. This score will be applied to the entire EDC population in future studies to determine the effect of insulin resistance on complications.