PH1 is caused by deficiency of the liver-specific peroxisomal enzyme alanine: glycoxylate aminotransferase (AGT). Early onset with progressive renal failure and systemic oxalosis is typical. We report a case of a 42 year-old man with PH1 in whom liver biopsy and DNA-analysis showed reduced AGT-activity and homozygosity for the polymorphism C154T and the point mutation G630A. The patient seems to respond to pyridoxine treatment. We suggest that clinical suspicion of PH1 be pursued with a diagnostic liver biopsy.