ABSTRACT— Cerebral function was studied in patients with non-cirrhotic portal fibrosis who had no clinically detectable neurological abnormality, 14 before and 29 after a proximal lienorenal shunt operation. In each patient electroencephalography (EEG) and psychometric tests (the number connection test, construction of a five-pointed star and the reverse counting test) were performed. Psychometric tests were also done in an equal number of matched, healthy controls. Subclinical encephalopathy was diagnosed when any of these tests was abnormal. In the unoperated group the EEG was normal in all patients and there was no difference in the psychometric test results between patients and healthy controls. After portosystemic shunt operations, the EEG was abnormal in 10%, the number connection test in 38%, construction of a five-pointed star in 19% and the reverse counting test in 30% of the patients. Detection of subclinical hepatic encephalopathy in such a high proportion of operated patients with non-cirrhotic portal fibrosis suggests that the surgical procedure and its haemodynamic consequences per se could have been responsible.