['To assess the ability of reactive hyperemia-peripheral artery tonometry (RH-PAT) to serve as a surrogate marker of endothelial dysfunction in children with type 1 diabetes (T1D).', 'Forty-four children with T1D [age 14.6 +/- 2.7 yr; duration of diabetes 6.01 +/- 4 yr; range of diabetes duration 1-16 yr; and hemoglobin A1c (HbA1c) 8.34 +/- 1.2%] and 20 children without diabetes (age 14.1 +/- 1.5 yr) underwent RH-PAT endothelial function testing after an overnight fast. Height, weight, body mass index (BMI), blood pressure (BP), fasting lipid profile, and glucose level were determined in each child. Children with T1D underwent a second RH-PAT study 4 wk after their initial study to determine the intrapatient variability of the technique.', 'Children with T1D had endothelial dysfunction as evidenced by lower mean RH-PAT scores (1.63 +/- 0.5) when compared with children without diabetes (mean RH-PAT score 1.95 +/- 0.3) (p = 0.01). Repeat RH-PAT scores were predicted by initial RH-PAT scores (p = 0.0025). Mean intrapatient standard deviation of RH-PAT score was 0.261 and mean coefficient of variation was 14.8. Variations in RH-PAT score were not explained by differences in glucose, HbA1c, BMI, systolic BP, diastolic BP, or lipids.'] Does peripheral artery tonometry demonstrate altered endothelial function in children with type 1 diabetes?