Only 2 patients with an oxysterol 7α‐hydroxylase deficiency caused by mutations of the cytochrome P450 7B1 (CYP7B1) gene have been reported; for both, the outcome was fatal. We describe the clinical and laboratory features, the hepatic and renal histological findings, and the results of bile acid and CYP7B1 gene analyses for a third patient. This Japanese infant presented with progressive cholestatic liver disease and underwent successful heterozygous living donor liver transplantation. Sources of relevant data included medical records, hepatic and renal histopathological findings, gas chromatography/mass spectrometry analyses of bile acids in serum and urine samples, and analyses of the CYP7B1 gene in the DNA of peripheral blood lymphocytes. Large excesses of 3β‐hydroxy‐5‐cholen‐24‐oic acid were detected in the patient's serum and urine. Cirrhosis and polycystic changes in the kidneys were documented. The demonstration of compound heterozygous mutations (R112X/R417C) of the CYP7B1 gene led to the diagnosis of an oxysterol 7α‐hydroxylase deficiency. After liver transplantation with an allograft from a heterozygous living donor (the patient's mother), the features of decompensated hepatocellular failure abated, and the renal abnormalities were resolved. In conclusion, we report the first Japanese patient with an oxysterol 7α‐hydroxylase deficiency associated with compound heterozygous mutations of the CYP7B1 gene; in this patient, liver transplantation with an allograft from a parental donor was effective. Liver Transpl 17:1059–1065, 2011. © 2011 AASLD.