Ornithine transcarbamoylase (OTC) deficiency is the most common hereditary urea cycle disorder. It is an X-linked recessive disorder that usually presents with encephalopathy and hyperammonaemia. We report a 14-month-old female carrier of OTC deficiency, who presented with a history of intermittent vomiting for 5 weeks and irritability and lethargy for 1 week. She was found to be in acute liver failure, with elevated transaminases, coagulopathy and a consistently low urea. Identifying an OTC mutation and ruling out other possible causes of acute hepatic failure confirmed the diagnosis. She was placed on low-protein diet supplemented with essential amino acids, and her liver enzymes, hyperammonaemia and coagulopathy corrected. Three other female patients have been reported with OTC deficiency presenting with severe cryptogenic hepatitis; our patient is unique in that the presentation of her disease was dominated by acute liver failure on a back ground of normal growth and development, no liver enlargement, and mild hyperammonaemia. OTC deficiency should be considered in the differential diagnosis of infants presenting with acute hepatocellular dysfunction, especially in females.