BACKGROUND: QT-wave abnormalities have been detected in type 1 diabetes mellitus (T1DM). Prolongation of the heart rate corrected QT interval (QTc) has been associated with cardiovascular mortality. We evaluated how often QT/QTc abnormalities are present in youth with T1DM and if they are associated with disease parameters.METHODS: Sixty-two T1DM youngsters and equal age- and gender-matched controls were studied. Demographic, anthropometric, and laboratory data were determined. QT was measured on a 12-lead resting electrocardiogram. QTc was calculated using Bazett's formula.RESULTS: T1DM patients had significantly longer QT/QTc than controls, but significance disappeared after adjustment for confounders. Abnormally prolonged QTc≥440 ms was observed six times more frequently in those with T1DM. QT was correlated with age, age at disease onset, but not with glycated hemoglobin or diabetes duration; QTc was only correlated with pubertal stage.CONCLUSIONS: T1DM youths have a sixfold increased risk for QT/QTc prolongation and should have regular follow-up for cardiac autonomic dysfunction.