The aim of this study was to investigate the influence of body mass on autonomic nerve function in persons with type 2 diabetes. Towards this aim we studied two groups of diabetic persons. Group 1: n = 30 lean (mean age 57.2+/-12.5 years, body mass index (BMI) 22.5+/-1.8 kg/m2]. Group 2: n = 35 overweight and obese (age 52.3+/-10.3 years, BMI 28.8 + 3.2 kg/m2). Autonomic neuropathy (DAN) was assessed using the battery of the five classical tests. DAN was diagnosed when at least two of the five tests were abnormal. Abnormalities of the heart rate based tests were considered as indication of parasympathetic and of blood pressure changes as indication of sympathetic dysfunction. The prevalence rates of DAN were not different between group 2 and group 1 (54.2 and 53.3%, respectively, P = 0.54). The same was valid for the rates of parasympathetic and sympathetic dysfunction in the studied groups (51.4 and 53.3% (P = 0.87) in group 2 and 34.2 and 33.3% (P = 0.93) in group 1, respectively). When the values of the arithmetic expression of each single autonomic function test were compared, no significant difference could be shown between the studied groups. In addition, no significant correlation was found between BMI and indices of DAN. These data indicate that moderate increase of body mass does not affect autonomic function in persons with type 2 diabetes.