Paracetamol poisoning is the most common cause of acute liver failure (ALF) in Western Europe, Australia and USA. The N-acetyl derivative of the amino acid cysteine (NAC) serves as a precursor to the production of glutathione and is the treatment of choice in early paracetamol toxicity. Patients with hyperacute or acute liver failure often require significant volumes of fluid resuscitation. Patients with liver failure are prone to hypoglycaemia. Liver failure leads to a loss of synthetic function of hepatocytes and reduction of coagulation factors, and international normalized ratio (INR) is a very important prognostic factor. The complications of liver failure include hepatic encephalopathy, intracranial hypertension, renal failure and adrenal dysfunction. In a selected group of patients liver transplantation is the treatment of choice. Overall survival, without transplantation, is about 40% following the onset of ALF. Acute on chronic liver failure represents the decompensation of otherwise stable chronic liver disease.