Progressive familial intrahepatic cholestasis (PFIC) is a lethal inherited childhood cholestasis of hepatocellular origin. Different subtypes of PFIC have been described according to serum gamma-glutamyl transpeptidase (GGT) activity. There is currently no effective medical therapy available for children with PFIC. We report on 39 patients with PFIC who received ursodeoxycholic acid (UDCA) orally (20-30 mg/kg b.w./day) for a period of 2 to 4 years. Group 1 (n = 26) consisted of children with normal GGT activity, and group 2 (n = 13) of children with high GGT activity. Within group 1, liver tests normalized in 11 children, improved in 5, and stabilized or worsened in 10. Within group 2, liver tests normalized in six children, improved in four, and stabilized or worsened in three. Improvement of parameters was associated with an enrichment of the circulating pool of bile acids with UDCA. Hepatosplenomegaly and pruritus disappeared or diminished in children in whom liver tests normalized. In nine of these children, liver tests worsened and normalized again after stopping and restarting UDCA. Liver histology assessed in four children after normalization of liver tests and 2 years of treatment showed a decrease in fibrosis. We conclude that UDCA should be considered in the initial therapeutic management of children with PFIC, because it appears effective in resolving or improving the liver function and the clinical status of a fair proportion of children. Chronic UDCA therapy might thus avoid the need for liver transplantation in some children with PFIC.