To evaluate the autonomic nervous control of the heart in patients with systemic sclerosis (SSc), spontaneous heart rate variability was investigated by means of time-domain and spectrum analysis of 24 h ECG ambulatory recordings in 30 SSc patients (four males, aged 45.2 +/- 9 yr, mean +/- S.D., range 27-60) and 30 age-matched healthy subjects. A significantly higher heart rate (P < 0.01) and lower circadian and spectral indices of heart rate variability (P < 0.01) were observed in SSc patients, compared with controls. A predictive value of age (P = 0.002), tachycardia (P = 0.002), circadian heart rate variability (P = 0.0025) and spectral power values (P = 0.005) for patient mortality was found. Moreover, the relative risk of death was higher (P = 0.05) in older subjects with circulating anti-Scl70. These abnormalities, detectable by a feasible, non-invasive diagnostic approach, indicate the presence of autonomic cardiac neuropathy in SSc patients.