Summary The most sensitive index of hepatic encephalopathy in 29 patients following a porta-caval shunt appeared to be the assessment of a close relative who had known the patient pre-operatively. They noticed that 19 of the 20 patients were mentally slower; 11 were markedly aggressive and 8 had become placid and uncaring about family problems. Only 9 of these patients had clinical encephalopathy as judged by two independent observers, 14 had a prolonged trail test and 8 produced an abnormal five-pointed star. Eight patients were forced to retire prematurely after the operation due to ill health and 20 felt that their marriage had deteriorated. Eighteen of the 29 patients had a lie score on the Eysenck personality questionnaire (an index of ‘social naïvety’) which was more than one standard deviation above the mean value for a large control group (P < 0.01). This did not correlate with other measurements of encephalopathy, but 8 out of the 11 patients who exhibited aggressive behaviour had an abnormal score.