OBJECTIVE: The purpose of this study was to evaluate forehead sympathetic skin response (SSR) and demonstrate any differences with extremity SSR in determining autonomic nervous system (ANS) involvement in patients with Parkinson\'s disease (PD). METHODS: Twenty early stage, 20 advanced stage idiopathic PD patients and 20 healthy controls participated in this study. SSR of forehead, hands and feet, heart rate variability (HRV), orthostatic intolerance, QT intervals and dysautonomic symptoms were evaluated. RESULTS: Absent forehead SSR was determined unilaterally in 4, bilaterally in 7 early stage patients, and unilaterally in 4, bilaterally in 8 advanced stage PD patients; there was significant difference between early and advanced stage PD and control groups in terms of the lack of SSR (p=0.000). Absent extremity SSR was determined in at least 1 extremity of 3 advanced stage PD patients, and none of the early stage PD patients. No difference was noted in HRV at rest between early and advanced stage PD and control groups (p=0.218); but HRV at deep breathing was lower in both early and advanced PD patients compared to controls (p=0.014, p=0.002, respectively). CONCLUSION: Forehead SSR is more sensitive in determining ANS dysfunction not only in late but also in early stage of PD. SIGNIFICANCE: With further supportive research, forehead SSR might be used as a simple diagnostic electrophysiological test in the early diagnosis of ANS dysfunction enabling proper treatment and increasing the quality of life of PD patients.