Acute on chronic liver failure (ACLF) is associated with high short term mortality. We aimed to evaluate the prevalence, predictors and impact of bacterial infection in ACLF. Consecutive hospitalized patients with cirrhosis and acute decompensation (AD), from January 2011-March 2017, were included. Predictors of survival and infection were assessed. 572 patients with cirrhosis and AD were classified into 3 groups - no infection (group 1, n = 190, 33.2%), infection at admission/within 48 h (group 2, n = 298, 52.1%) and infection after 48 h (group 3, n = 84, 14.7%). Higher frequency of organ failures - kidney, brain, circulation and respiratory failure - were seen in groups 2 and 3 as compared with group 1 (P < 0.001 for all). Most common site of infection was lungs, followed by spontaneous bacterial peritonitis and urinary tract infection. The frequency of infection increased with higher ACLF grades. Among ACLF patients, on Cox-proportional multivariate analysis, presence of infection was associated with significantly higher mortality [group 2 (HR 2.93; 95%CI, 1.97-4.38, P < 0.001) and group 3 (HR 1.84; 95%CI, 1.16-2.91, P = 0.009)], as compared with group 1. On multivariate logistic regression analysis, advanced hepatic encephalopathy and elevated total leucocyte count were independently associated with development of infection. Infections are common in ACLF, and associated with poor outcome. Copyright © 2018 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.