Subclinical impairment of the peripheral nervous system (PNS) is frequent during HIV infection. Nevertheless, little attention has been given to the autonomic nervous system (ANS). We undertook a prospective study of the ANS, exploring 55 HIV+ subjects with non-invasive functional tests for the cardiac ANS. We also made a quantitative study of thermic (small fibers) and vibratory (large fibers) sensibilities. The results do not show any statistically significant difference between HIV+ subjects and control subjects or between HIV+ subjects of groups I, II and III and those of group IV of the CDC classification. However, an individual analysis comparing the results of the infected subjects with those of the control group indicated the presence of functional abnormalities of the ANS (small fibers) in 34.5% of HIV+ patients with an equally frequent impairment of the thermic perception (small fibers) and of the vibratory perception (large fibers). Moreover, the signs of subclinical dysautonomia were more frequent in group IV (48.3%) than in groups I, II and III (19%) showing a progressive accentuation of the troubles during the course of the infection.