BACKGROUND Crigler-Najjar syndrome (CNS) is a very rare disease characterized by severe indirect hyperbilirubinemia from birth with normal liver function. It may cause kernicterus at any age. This disease is due to a total or partial deficiency of the UDP-glucuronosyltransferase enzyme caused by a mutation of the five exons of the ULT1A1 gene. METHODS We reviewed the clinical outcomes of 7 children diagnosed with CNS between 1987 and 2004. RESULTS There were three boys and four girls (two of which were homozygote twins). Two children had familial consanguinity. Three out of the six families had another healthy child. The mean follow-up was 8.3 years (14 months-17 years). In all patients, jaundice was detected in the first 3 days of life. The children were admitted to hospital between the fourth and the sixtieth day of life with jaundice and indirect bilirubin levels of between 12.5 and 32 mg/dl. In all patients, hemolysis was ruled out and hepatic function was normal. The diagnosis was based on genetic study in 4 patients, on inactive UGT enzyme in liver in 1 patient, and on clinical features exclusively in 2 patients. Treatment consisted of phenobarbital and phototherapy from 8 to 16 hours a day in all patients except three. Associated calcium salts were found in 5 patients and cholestyramine was found in two. Two patients developed kernicterus. Two underwent liver transplantation and bilirubin levels became normal. The remaining patients maintained indirect bilirubin from 15 to 25 mg/dl with no associated neurological alterations. CONCLUSIONS Patients with CNS are at greater risk of developing kernicterus, mostly associated with indirect bilirubin levels of around 25 mg/dl. Phototherapy is very useful in these patients but the only definitive treatment is liver transplantation.