OBJECTIVE: We aimed to determine and compare HRV parameters in poorly and well controlled type 2 diabetes. 54 normotensive type 2 diabetes patients without clinical signs of CAN were enrolled; 29 poorly controlled (HbA1c >/= 7%) and 25 controls matched for age, sex and BMI. HRV analysis was performed using 24-h ambulatory ECG, with automatic estimation of the time and frequency domain ranges. Comparisons were performed using Mann-Whitney test. RESULTS: We included 54 participants (26 males) aged 56 years [43-62], with known duration of diabetes 3 years [1-7]. HbA1c was 10.1% [9.1-11.9] vs 5.3% [5.1-6.3] (p < 0.001). Blood pressure was 126 mmHg [121-130] vs 124 mmHg [113-133] in the poorly controlled group and the well-controlled group respectively (p = 0.5). 24-h mean heart rate was significantly higher in poorly controlled vs well controlled patients (79 bpm [77-83] vs 75 bpm [69-79], p = 0.006). In the time domain analysis, markers of the overall variability were lower and thus altered in the poorly controlled group (SDNN: 102 ms [90.5-111.1] vs 112.3 ms [104.4-131.2], p = 0.01 and SDANN 88 ms [72.9-99.7] vs 97.8 ms [91.8-114.5], p = 0.01). The frequency domain analysis showed trends towards lower values of sympathovagal balance markers in the poorly controlled group. Reduced HRV is associated with poorly controlled type 2 diabetes mellitus and may be an early marker in clinical practice.