PURPOSE: This study aimed to characterize the role of autonomic nervous system dysfunction in hot water epilepsy (HWE). Heart rate variability (HRV) has been established as a good index of cardio-autonomic regulation. METHODOLOGY: Forty-five patients with HWE (age: 24.6+/-10.1 years; M:F=37:8) and 45 age and gender matched controls (age: 24.17+/-10.37 years; M:F=37:8) were studied. Five minutes resting lead II electrocardiogram (ECG) was obtained (AD instruments) under standard conditions and analyzed for time and frequency domain HRV parameters using LabChart software. RESULT: Patients with hot water epilepsy showed significant increase in LF nu (Low frequency normalized unit) and LF/HF denoting an interictal increase in sympathetic activity. In addition, reductions were noted in parasympathetic function [RMSSD (root mean square successive difference of RR intervals), HF (High frequency) nu and LF/HF]. CONCLUSION: This study has demonstrated an impaired sympatho-vagal balance characterized by increased sympathetic activity and reduced parasympathetic activity in patients with HWE. The present study supports the notion that the hypothalamus is involved in both, the pathogenesis of HWE and autonomic regulation.