The records of 52 children with Niemann-Pick disease type C were reviewed to establish whether the disease process and outcome varied with the initial clinical pattern; 34 children (65%) had cholestatic liver disease and hepatosplenomegaly in infancy; 18 were seen at a mean age of 4 years with splenomegaly or neurologic disease or both. Of the 34 children with early cholestatic liver disease, three died in the neonatal period; cholestasis and hepatomegaly subsided in the remaining 31 children, although splenomegaly persisted. Of these 31 children, 15 had persistent liver disease with elevated aminotransferase values. Serial liver biopsy specimens showed that 3 of the 15 children had normal architecture and 12 had hepatic fibrosis, with progression to cirrhosis in 5. No other significant morbidity or additional deaths were associated with the liver disease. The clinical importance of persistent liver disease was overshadowed by the subsequent development of severe neurologic disease. There was no difference in the age at onset of the disease (mean, 4.5 years) or in the pattern of neurologic disease, including supranuclear ophthalmoplegia, whether or not the child had early liver disease. Overt neurologic disease has not yet developed in seven surviving children with liver disease at onset. Sixty-seven percent of children died during the study; the main cause of death was bronchopneumonia. We conclude that the diagnosis of Niemann-Pick disease type C should be considered in patients with unexplained neonatal hepatitis, especially if splenomegaly is a persistent feature. Because liver biopsy specimens may not demonstrate storage cells, bone marrow aspiration to detect the characteristic storage cells is recommended in such patients.