AIMS: Because reduction in baroreceptor sensitivity (BRS) has been associated with hypertension in the normal population and with increased cardiovascular morbidity and mortality in patients with diabetes mellitus, we measured BRS in a patient cohort of children with type 1 diabetes mellitus. METHODS: Two hundred and eight children (150 patients with type 1 diabetes mellitus, mean age 13.9 +/- 2.8 years, 70 boys, mean HbA(1c) 7.8 +/- 1.4%; and 58 healthy controls, mean age 14.1 +/- 3.1 years, 32 boys) were studied. BRS and heart rate variability (HRV) were analysed from a short-time ECG and BP recording using the sequence method (BRS) and the frequency domain method (HRV). RESULTS: There were 111 of 150 patients (74%) and 5 of 58 controls (8.6%) that showed impaired BRS. Mean BRS differed significantly between patients and controls (18.4 +/- 7.2 vs 25.8 +/- 8.2 ms/mm, p < 0.001). BRS correlated inversely with systolic BP (r = -0.23, p = 0.009) and was related to diabetes duration (r = -0.194, p = 0.027). Analysis of HRV showed greater sympathetic and less parasympathetic influence in patients than in controls (low frequency/high frequency ratio 1.3 +/- 0.8 vs 0.9 +/- 0.6, p < 0.05); the low frequency/high frequency ratio was inversely correlated with BRS (r = -0.28, p = 0.001). CONCLUSIONS/INTERPRETATION: Diabetic children show reduced BRS. In our patient group, the single risk factor for this finding was found to be the disease duration. The degree of BRS impairment was related to the degree of autonomic dysbalance.