Automated analysis of the electroencephalogram as an objective measurement of hepatic encephalopathy for the individual patient was investigated. The mean dominant frequency of patients with grades 0 and 1 hepatic encephalopathy was in the normal range (greater than or equal to 6.4 Hz); grade 1 hepatic encephalopathy, however, was characterized by abnormal relative power of theta activity of more than 35%. Twelve out of 34 patients with clinical grade 0 hepatic encephalopathy also had an elevated power of theta activity and probably therefore latent hepatic encephalopathy. Patients with grades 2, 3 and 4 hepatic encephalopathy had a low mean dominant frequency (less than 6.4 Hz) and could be identified by a biphasic power spectrum (theta and delta peaks, grade 2) or by a high power of delta activity (greater than or equal to 70%, grade 3-4). We conclude that automated EEG analysis based on the parameters mean dominant frequency and the relative powers of the delta and theta band is very suitable for objective classification of hepatic encephalopathy in individual patients.