A liver transplant was performed on a 4-year-old female in liver failure caused by hereditary tyrosinaemia, with hepatocellular carcinoma following a negative evaluation for metastases. However, serum alpha-fetoprotein levels never returned to normal after the surgery. Urinary succinylacetone (SA) was detected in her urine prior to transplantation despite strict adherence to a low-tyrosine diet. Other patients with severe liver disease awaiting liver transplantation do not excrete SA in the urine. She continued to excrete SA during the postoperative period despite normal liver functions. Oral tyrosine loading resulted in significant elevation of SA excretion. Possible explanations for this observation and clinical and therapeutic relevance are discussed.