Acute liver failure is a potentially deadly condition that affects about 2000 Americans each year. Most often, liver failure develops over a period of years as an insult to the liver (such as alcohol abuse or infection with hepatitis virus) slowly damages it. Less commonly, liver failure is acute, meaning that it occurs over a period of days or weeks. The things that can cause acute liver failure include hepatitis virus infections, drugs, pregnancy, autoimmune disease, and sudden low blood flow to the liver. Little is known about how often each of these things is responsible for acute liver failure in the United States. Information about the causes and outcomes of acute liver failure would be helpful to doctors who care for patients with this condition.