OBJECTIVES: Acute-on-chronic liver failure (ACLF) is well-studied in adults and characterized by decompensated cirrhosis, multi-organ failure, and early mortality. Studies of ACLF in children are limited. We sought to characterize the prevalence and clinical factors associated with pediatric ACLF (PACLF). METHODS: A retrospective review of children 3 months to 18 years listed for liver transplantation and hospitalized for decompensated cirrhosis between January 2007 and December 2017 at a single pediatric hospital. Primary outcome was the development of PACLF, characterized as failure of at least 1 extrahepatic organ (mechanical ventilation, renal replacement therapy, vasoactive medications, grade III/IV hepatic encephalopathy). Characteristics were recorded for each hospitalization. RESULTS: Sixty-six patients had 186 hospitalizations with mean age at admission 4.0 ± 5.6 years and diagnosis of biliary atresia (BA) in 65%. PACLF developed in 20 patients during 23 hospitalizations (12%) and respiratory failure was most common (17/23, 74%). Duration of intensive care unit stay, 13.1 ± 1.2 versus 0.6 ± 0.6 days (P < 0.001) and length of stay, 24.3 ± 5.0 days versus 7.9 ± 1.9 days (P = 0.003) were longer in PACLF compared with non-PACLF. Mortality during PACLF hospitalizations was 22%. Clinical factors associated with PACLF were reported from a generalized linear mixed model and included increased admission creatinine (P < 0.0001), increased aspartate aminotransferase (AST) (P = 0.014), increased international normalized ration (INR) (P = 0.0015), and a positive blood culture (P = 0.007). CONCLUSION: In this pediatric series, PACLF developed in 12% of hospitalizations and mortality was high. Admission creatinine, AST, INR, and presence of a positive blood culture were associated with PACLF development.