A patient with hepatic cirrhosis due to Alpers disease is described who had a significantly raised plasma alanine aminotransferase (ALT) activity of 247 U/L which returned to normal (18 U/L) shortly after commencing treatment with the anticonvulsant drug, vigabatrin. Previous studies have reported smaller reductions in plasma ALT activity due to vigabatrin, generally in patients with normal liver function. This case demonstrates that vigabatrin may also reduce markedly elevated ALT activity to the normal range in patients with documented liver disease. Plasma ALT activity cannot be used as an index of liver cell damage in patients receiving vigabatrin.