Four children underwent living related liver transplantation because of Crigler-Najjar syndrome type 1. Three were infants aged 2, 8(1/2), and 15 months, and weighed 5, 8, and 10 kg, respectively. Pretransplantation unconjugated bilirubin concentration was 22 to 30 mg/dL despite 12 to 14 hours of phototherapy daily. Patient 1, the 2-month-old infant, with unconjugated bilirubin concentration of 30 mg/dL, had a high-pitched cry, suggestive of bilirubin encephalopathy; results of neurologic examination were normal. Plasmapheresis and urgent liver transplantation were performed. Patient 4, a 13-year-old girl, had learning difficulties at school and attended a special class. Three patients received left lateral liver segments, and 1 patient received a left lobe. Biliary reconstruction was completed with duct-to-duct anastomosis. Bile leakage developed at the anastomosis in 2 patients, which was treated successfully with cholangioplasty. In all patients, the unconjugated bilirubin concentration normalized by day 1 posttransplantation, and no phototherapy was necessary. After transplantation, the 2-month-old infant with suspected encephalopathy exhibited hypotonia, spasticity of the lower extremities, and lack of head control. He died after vomitus aspiration during sleep at 10 months posttransplantation. The other 3 patients are alive with normal neurodevelopmental milestones. Irreversible brain damage may occur early in the course of Crigler-Najjar syndrome type 1. Urgent treatment including plasmapheresis, exchange transfusion, phototherapy, and liver transplantation may not reverse brain damage. Young infants must be evaluated carefully for subtle signs and symptoms of bilirubin encephalopathy. Liver transplantation is curative if performed before development of neurologic dysfunction.