Crigler-Najjar type 1 disease (CNS1) is the result of a genetic defect, leading to complete functional loss of an enzyme which glucuronidates bilirubin. As a consequence, unconjugated bilirubin accumulates and may cause kernicterus, the most serious complication in adolescents. Phototherapy effectively adjusts bilirubin levels less than critical concentrations over many years but become less effective in elder children. Therefore, liver transplantation must be performed as definite therapy in these patients to avoid irreversible neurological deficits. Two brothers with CNS1, one without neurological deficits and one with moderate brain injury underwent orthotopic split liver transplantation from the same donor. The intra- and postoperative course of both patients was uneventful. Bilirubin levels normalized after transplantation in both recipients. Furthermore, mental and physical development considerably improved upon transplantation in the brother with neurological dysfunction. Therefore, orthotopic liver transplantation in CNS1 patients should be performed early enough to avoid irreversible brain damage, i.e., as a prophylactic procedure.