Acute liver failure patients with a persistence of hyperammonemia are at an increased risk of intracranial hypertension due to development of brain oedema. In vitro studies of brain tissue and cell cultures that indicates that exposure to ammonium inhibits enzymatic activity in the tricarboxylic acid cycle, induces substrate depletion through marked glutamate utilization for glutamine synthesis and leads to mitochondrial dysfunction. In patients with acute liver failure cerebral microdialysis studies show a linear correlation between the lactate to pyruvate ratio and the glutamine concentration, as well as to some of the adenosine triphosphate degradation products. However, clinical observations of cerebral exchange rates of oxygen, glucose, lactate and amino acids challenge the interpretation of these findings. In this review the conflicting data of cerebral metabolism during acute liver failure is discussed.