OBJECTIVE: To assess the utility of whole-exome sequencing (WES) in a sibling pair with undetermined liver disease and describe the phenotype associated with mutations discovered therein. STUDY DESIGN: Next-generation WES was performed on 2 siblings (S1 and S2) who were born to nonconsanguineous parents of European extraction. Both siblings developed cirrhosis of indeterminate etiology and required liver transplantation; S1 at 7 months and S2 at 22 months. RESULTS: Sequencing of germline DNA identified compound heterozygous mutations in PPP1R15B resulting in increased levels of phosphorylated eukaryotic translation initiation factor 2alpha. CONCLUSIONS: The first demonstration of PPP1R15B associated with liver disease expands the phenotypic spectrum of PPP1R15B related diseases. Our findings validate the application of WES in the diagnosis of children with undetermined liver disease. Understanding the genetic basis of liver disease may allow the development of targeted therapies for treatment and adequate counseling of families.