© 2016 by ESPGHAN and NASPGHAN. Objectives: Hepatic encephalopathy (HE) is challenging to identify in children with acute liver failure and was not a requirement for enrollment into the Pediatric Acute Liver Failure Study Group (PALFSG). The outcomes of PALFSG participants presenting with and without HE are presented. Methods: PALFSG participants were classified based on daily assessment of HE during the first 7 days following study enrollment: group 1 - never developed HE; group 2 - no HE at enrollment with subsequent HE development; and group 3 - HE at study enrollment. Clinical and biochemical parameters and outcomes of death, spontaneous recovery, or liver transplantation were compared between groups. Results: Data from 769 PALFSG (54% boys; median age 4.2 years; range 0-17.9 years) participants were analyzed, with 277 in group 1 (36%), 83 in group 2 (11%), and 409 in group 3 (53%). Mortality occurred in 11% of all participants and was highest among group 3 participants who demonstrated persistent grade III-IV HE (55%) or showed progression of HE (26%). Eleven (4%) group 1 participants died within 21 days of enrollment. Spontaneous recovery was highest in group 1 (79%) and lowest in group 2 (25%; P<0.001). Conclusions: Mortality 21 days after enrollment was highest in participants enrolled with severe HE (grades III or IV) or demonstrating HE progression. Four percent of participants without recorded clinical HE in the 7 days after enrollment, however, died within 21 days. Improved assessment of neurological injury and pediatric acute liver failure prognostication schema are needed.