Cerebral blood flow autoregulation is lost in patients with severe liver cirrhosis. The cause of this is unknown. We determined whether autonomic dysfunction was related to impaired cerebral autoregulation in patients with cirrhosis. Fourteen patients with liver cirrhosis and 11 healthy volunteers were recruited. Autonomic function was assessed in response to deep breathing, head-up tilt and during 24-h Holter monitoring. Cerebral autoregulation was assessed by determining the change in mean cerebral blood flow velocity (MCAVm, transcranial Doppler) during an increase in blood pressure induced by norepinephrine infusion (NE). The severity of liver disease was assessed using the Child-Pugh scale (class A, mild; class B, moderate; class C, severe liver dysfunction).NE increased blood pressure similarly in the controls (27 (24-32) mmHg) and patients with the most severe liver cirrhosis (Child-Pugh C, 31 (26-44) mmHg, p=0.405 Mann-Whitney). However, the increase in MCAVm was greater in cirrhosis patients compared to the controls (Child-Pugh C, 26 (24-39) %; controls, 3 (-1.3 to 3) %; respectively, p=0.016, Mann-Whitney). HRV during deep breathing was reduced in the cirrhosis patients (Child-Pugh C, 6.0+/-2.0 bpm) compared to the controls (21.7+/-2.2 bpm, p=0.001, Tukey' test). Systolic blood pressure fell during head-up tilt only in patients with severe cirrhosis. Our results imply that cerebral autoregulation was impaired in the most severe cases of liver cirrhosis, and that those with impaired cerebral autoregulation also had severe parasympathetic and sympathetic autonomic dysfunction. Furthermore, the degree of liver dysfunction was associated with increasing severity of autonomic dysfunction. Although this association is not necessarily causal, we postulate that the loss of sympathetic innervation to the cerebral resistance vessels may contribute to the impairment of cerebral autoregulation in patients with end-stage liver disease.