Background: The definition of acute liver failure (ALF) usually implies no previous liver injury. Though, some patients admitted to liver transplantation centers with the diagnosis of ALF are obese or have diabetes. Elevated liver enzymes were not recorded previously, and no signs of cirrhosis or prior decompensation of the liver function were ever present. Still, these patients differ from the “typical” ALF-patient. Goals: In this study, we aimed to confirm acute-on-chronic-liver failure (AOCLF) in patients diagnosed with ALF and to identify possible differences between ALF and AOCLF. Study: Patients were retrospectively recruited from all patients admitted to the University Hospital Essen with diagnosis of ALF between 2008 and 2015. Data of 163 patients were evaluated, resulting in a reclassification of 32 patients as AOCLF (remaining ALF: 131). Demographic and clinical data as well as serum parameters, including cell death markers, were correlated with clinical outcome. Results: Patients with AOCLF were significantly older, had a higher body mass index (BMI), and were more often male. The cause for liver failure in these patients differed significantly from patients who had an actual ALF. Significant differences were also found for serum liver enzymes. Outcome of patients did not differ between AOCLF and ALF. Though, lower BMI and MELD and higher AST and GLDH were predictors for a beneficial outcome. Conclusion: AOCLF is still commonly misdiagnosed as ALF. While clinical outcome does not significantly differ between ALF and AOCLF, risk factors for adverse outcome may significantly differ between these entities.