Background ‘Acute-on-chronic liver failure’ (ACLF) is characterised in a more advanced stage by liver failure associated with multiple other end-organ failure. The global clinical characteristics of this entity remain, however, ill-defined. Objective To characterise and evaluate the clinicopathological features of patients with ACLF compared with patients with chronic decompensated cirrhosis (CHD) in a prospective, homogeneous cohort of patients with histologically proven alcoholic cirrhosis from 2002 to 2007. Results In total 250 patients were screened (ACLF (n=70, 28%) and CHD (n=180, 72%)). Alcoholic liver disease was observed in respectively 61/70 (87%) of patients with ACLF and 72/180 (40%) of patients with CHD. After exclusion of 31 patients, 102 patients were studied: 54 with ACLF (median age 51 years; Child–Pugh 12±2; in-hospital mortality 46% (25/54)) and 48 patients with CHD (median age 53 years; Child–Pugh 10±2; in-hospital mortality 10% (5/48)). In the patients with ACLF who survived the hospital stay, the difference in transplant-free survival compared with patients with CHD tended to attenuate with time. At admission the apparent infection of patient groups was comparable but during hospitalisation infection occurred more frequently in patients with ACLF (31/53 (58%)) than in those with CHD (12/47=26%) (p=0.007). Early signs of infection, positive systemic inflammatory response syndrome (SIRS) criteria at admission and ductular bilirubinostasis (p=0.04), were early features that predicted outcome in ACLF. Conclusion Patients with ACLF have a high short-term mortality but those who survived the acute exacerbation show a long-term outcome comparable to that of patients with CHD. Infection is the most common cause of mortality in these patients. Positive SIRS criteria and ductular bilirubinostasis are early markers of ACLF and might allow more rapid identification of high-risk patients.