Heart rate variability (HRV) is a suitable diagnostic tool in identifying patients with autonomic nervous system (ANS) disorders even in pre-clinical stage. We have enrolled in this study all patients with large variety of connective tissue disorders, given the possibility of an involvement of ANS in these diseases. The study population consisted in eighty-five patients (68 females and 17 males), 35 of whom affected by systemic lupus erythematosus, 16 by rheumatoid arthritis, 14 by Sjogren syndrome, 12 by progressive systemic sclerosis, 3 by Behcet syndrome and 5 by antiphospholipid antibodies syndrome. The mean age ranged between 33.7 of patients with lupus erythematosus and 51.8 of those with Sjogren syndrome. As control, we enrolled healthy subjects of different age, divided into two groups, to rule out the aging as potential source of considered parameters alteration. The autonomic function has been evaluated by 24 hours ambulatory monitoring, using a Zymed 1210 Scanner with Zymed 3.74-PC 1990 software. We have considered: in the time domain, the standard deviation of the RR intervals average (SDNN) and the percentage of RR adjacent intervals differing each other more than 50 msec (pNN50); in the frequency domain, the low (LF) and high (HF) frequencies, the LF/HF ratio, and the total power (RT). The HRV parameters resulted abnormal in every type of the connective tissue diseases considered: particularly SDNN, pNN50, LF, HF and RT (p < or = 0.01). IN CONCLUSION: the results of our study suggest that autonomic neuropathy may be present in any kind of connective tissue disorders even in preclinical stage.