Aims: To conduct a clinical electrophysiologic evaluation of autonomic nervous system functions in patients with burning mouth syndrome and Parkinson disease and estimate the type and intensity of the autonomic dysfunction. Methods: The study involved 83 subjects-33 with burning mouth syndrome, 20 with Parkinson disease, and 30 controls. The BMS group included 27 women and 6 men (median age, 60.0 years), and the Parkinson disease group included 15 women and 5 men (median age, 66.5 years). In the control group, there were 20 women and 10 men (median age, 59.0 years). All patients were subjected to autonomic nervous system testing. In addition to the Low autonomic disorder questionnaire, heart rate variability (HRV), deep breathing (exhalation/inspiration [E/I] ratio), and sympathetic skin response (SSR) tests were performed in all cases. Parametric and nonparametric tests (ANOVA, Kruskal-Wallis, and Scheffe tests) were used in the statistical analysis. Results: The mean values for HRV and E/I ratios were significantly lower in the burning mouth syndrome and Parkinson disease groups. Significant prolongation of SSR latency in the foot was revealed in both burning mouth syndrome and Parkinson disease patients, and lowering of the SSR amplitude occurred in only the Parkinson disease group. The autonomic questionnaire score was significantly higher in burning mouth syndrome and Parkinson disease patients than in the control subjects, with the Parkinson disease group having the highest scores. Conclusion: In patients with burning mouth syndrome, a significant impairment of both the sympathetic and parasympathetic nervous systems was found but sympathetic/parasympathetic balance was preserved. The incidence and intensity of autonomic nervous system dysfunction was similar in patients with burning mouth syndrome and Parkinson disease, which may suggest some similarity in their pathogeneses.