Abstract Purpose Deterioration of consciousness is a critical situation for liver transplantation (OLT) recipients. The bispectral (BIS) index based on electroencephalographic parameters, is primarily used to monitor the depth of unconsciousness. The present study sought to assess the usefulness of posttransplant BIS index to monitor acute-on-chronic liver failure patients. Methods This 1-year retrospective study of 28 adult patients with acute-on-chronic liver failure was performed from July 2011 to June 2012, using post-transplant BIS monitoring. Results The mean patient age was 51 ± 8 years. Their mean pretransplant Child-Turcotte-Pugh score was 12.3 ± 1.4, and the mean Model for End-stage Liver Disease score, 36.4 ± 5.9. After OLT, the mean initial Glasgow Coma Scale (GCS) score and BIS index were 3.4 ± 1.7 and 43.5 ± 9.1, respectively. After 6 hours the mean GCS and BIS values rose to 8.6 ± 4.0 and 52.4 ± 10.3 and after 12 hours to 9.7 ± 3.4 and 61.3 ± 15.7 respectively. Eye opening in response to a voice occurred at a mean of 8.9 ± 6.7 hours after arrival in the intensive care unit regardless of graft function. The mean GCS and BIS values were 10.6 ± 2.8 and 69.1 ± 13.5, respectively. The endotracheal tube was removed after a median of 140 hours; 9 patients required a tracheostomy. Among them 2 died within the first 3 months after OLT. Conclusions BIS monitoring is a noninvasive, simple, easy-to-interpret method to measure consciousness among patients intubated with an endotracheal tube.