Background: Liver failure is a heterogeneous disease with varying aetiology, severity, complication rate and prognosis. Decreasing liver function in a previously healthy liver is called acute liver failure. A chronic disease or injury to the liver, for example viral or alcoholic hepatitis, can result in chronic inflammation, fibrosis and further development of cirrhosis. This disease can be well compensated or only slightly decompensated and nearly asymptomatic for a long time. An acute decompensation in the liver function in a patient with previously well compensated cirrhosis is called acute on chronic liver failure. This is often precipitated by infection or gastrointestinal bleeding and results in a dramatic lapse with serious complications and a high mortality. To identify prognostic factors in patients admitted with acute on chronic liver failure, a retrospective analysis of clinical and biochemical factors was performed.Material: Patients with acute on chronic liver failure admitted to Aker University Hospital from 01.01.04 to 01.03.08.Results: Many factors differed between those who died and those who survived. Infection as a precipitating factor and clinical findings as peripheral oedema, hepatic encephalopathy or splenomegali were more frequent amongst the patients who died. Albumine, bilirubine, creatinine, INR and platelets showed more pathological values amongst the patients who died. Those who died also had a higher MELD score.Conclution: Infection as a precipitating factor is associated with poor prognosis. High MELD score, pronounced and increasing liver failure, grave coagulopathy and increasing creatinine during hospital admission were associated with high mortality in our material.