To assess the autonomic system in obstructive sleep apnea syndrome (OSAS), the sympathetic skin response (SSR) and the R-R interval variation (RRIV) tests were studied in 34 OSAS patients and in 32 healthy controls. The aim of the study was to evaluate the sympathetic and parasympathetic system function in OSAS, to define the pattern of autonomic abnormalities found in SSR and RRIV in patients, and to analyze the usefulness of both tests in paraclinical assessment of the dysautonomia, compared with clinical symptoms and signs of autonomic nervous system involvement. The correlations between both autonomic tests results were also studied. In OSAS patients, SSR test results were abnormal in about 44% and RRIV results were abnormal in about 21% of patients. The mean values of parameters studied in SSR were significantly different in OSAS patients and controls (P < 0.05), whereas the differences between RRIV results were less important. The SSR and RRIV results in patients with mild apnea (Apnea/ Hypopnea Index (AHI) < 15) were more frequently within normal limits if compared with those of patients with severe apnea, but without reaching statistical significance. The clinical studies results (according to the Autonomic Symptoms Questionnaire) were related to the SSR results (p < 0.05 on chi and Fisher exact test). According to these results, SSR and RRIV are simple paraclinical electrophysiologic tests that confirm clinical dysautonomia. They may be useful as screening tests for assessment of dysautonomia in OSAS.