Acute liver failure is a rare but fatal condition characterized by rapid deterioration of liver function resulting in coagulopathy and altered mentation in patients without known liver disease. The three most common causes of liver failure in Korea are hepatitis B virus, exposure to certain herbs, and hepatitis A virus. Because the cause of liver failure is the most important prognostic factor, the etiology of liver failure should be evaluated as the initial step in the assessment of affected patients. Patients with acute liver failure should be intensively monitored and treated for various secondary conditions that may occur or have already developed, including cerebral edema, seizures, hemodynamic instability, renal failure, infection, bleeding, and metabolic disturbances. Although treatment with N acetylcysteine has shown a survival benefit in patients with mild hepatic encephalopathy, the overall mortality rate associated with acute liver failure is high unless patients undergo liver transplantation, prompting patients and physicians to be prepared for transplantation. Therefore, patients who are suspected to have, or who have been diagnosed with, acute liver failure should be transferred to a transplant facility and be prepared for liver transplantation while they undergo intensive monitoring and medical treatment.