The value of isolated liver transplantation in primary hyperoxaluria type 1 (PH1) and its timing are controversial. Two children with PH1 were followed up for 6 years after liver transplantation. A boy aged 5 years with a glomerular filtration rate (GFR) of 65 ml/min/1.73 m2 at the time of transplantation subsequently showed regression of calcium deposits in the kidneys, but GFR slightly declined, probably related to cyclosporin A toxicity. A girl with a severe neonatal form of PH1 received a liver at the age of 2 years when GFR had already declined to about 15 ml/min/1.73 m2 and extrarenal manifestations (bones, eyes) were present. In spite of these and further complications post-transplantation GFR stabilized. Growth failure was efficiently treated by growth hormone. Plasma and urinary oxalate concentrations, however, remained increased. It is suggested that in PH1 liver transplantation should be considered only if GFR is not rapidly declining and stays above 30 ml/min/1.73 m2. For an individual decision the different risks of liver transplantation and of combined kidney-liver transplantation as well as the possible benefits from previous conservative treatment must be considered.