OBJECTIVE: Anorexia nervosa (AN) is considered to have a significant risk for sudden death because of cardiac complications, and abnormalities of the autonomic nervous system might be a cause of cardiac dysfunction. The aim of this study was to investigate autonomic nervous system function in AN patients by analyzing heart rate variability (HRV), blood pressure variability (BPV), and baroreflex sensitivity (BRS). METHODS: The subjects were 32 AN patients without other psychiatric comorbidities and 37 healthy controls. Beat-to-beat R-R interval and systolic blood pressure recorded in the supine position were analyzed using power spectral analysis and cross-spectrum analysis to quantify the frequency domain properties of HRV, BPV, and BRS. In addition, detrended fluctuation analysis was used to quantify the fractal correlation properties from the scaling exponent alpha1 of HRV. RESULTS: High frequency power and total power of HRV and BRS were significantly higher in AN patients and low frequency power of BPV, low frequency/High frequency ratio of HRV, and the scaling exponent alpha1 of HRV were significantly lower in AN patients, compared with controls. CONCLUSIONS: These findings suggest that AN patients have reduced cardiovascular sympathetic nervous responsiveness, increased parasympathetic nervous responsiveness, and increased complexity of the interbeat interval time series compared with healthy controls. Regarding the relationship to prognosis of AN, the study showed conflicting results, and further prospective studies are needed to determine if these results are related to high mortality in AN patients.