Abstract Background and aims Acute-on-chronic liver failure (ACLF) is considered a main prognostic event in patients with chronic liver disease (CLD). We analyzed the 28-day and 90-day mortality in ACLF patients with or without underlying cirrhosis enrolled in the ACLF Research Consortium (AARC) database. Methods A total of 1,621 patients were prospectively enrolled and 637 (39.3%) of these patients had cirrhosis. Baseline characteristics, complications and mortality were compared between patients with and without cirrhosis. Results Alcohol consumption was more common in cirrhosis than non-cirrhosis (66.4% vs. 44.2%, p < 0.0001), while non-alcoholic fatty liver disease/cryptogenic CLD (10.9% vs 5.8%, p < 0.0001) and chronic HBV reactivation (18.8% vs 11.8%, p < 0.0001) were more common in non-cirrhosis. Only 0.8% of patients underwent liver transplantation. Overall, 28-day and 90-day mortality rates were 39.3% and 49.9%, respectively. Patients with cirrhosis had a greater chance of survival compared to those without cirrhosis both at 28-day (HR = 0.48; 95% CI 0.36–0.63, p < 0.0001) and 90-day (HR = 0.56; 95% CI 0.43–0.72, p < 0.0001), respectively. In alcohol CLD, non-cirrhosis patients had a higher 28-day (49.9% vs. 23.6%, p < 0.001) and 90-day (58.4% vs. 35.2%, p < 0.001) mortality rate than cirrhosis patients. ACLF patients with cirrhosis had longer mean survival than non-cirrhosis patients (25.5 vs. 18.8 days at 28-day and 65.2 vs. 41.2 days at 90-day). Exaggerated systemic inflammation might be the reason why non-cirrhosis patients had a poorer prognosis than those with cirrhosis after ACLF had occurred. Conclusions The 28-day and 90-day mortality rates of ACLF patients without cirrhosis were significantly higher than those with cirrhosis in alcoholic CLD. The presence of cirrhosis and its stage should be evaluated at baseline to guide for management. Thai Clinical Trials Registry, TCTR20191226002.