Infantile oxalosis is a rare, autosomal recessive disorder. We present three unrelated cases of infantile oxalosis and their families, emphasizing its place as a cause of acute renal failure in infancy, and showing the clinical heterogeneity of the disease within the same family. The affected infants (two males, one female) were 2.5, 3.5, and five months old. Two families had first degree parental consanguinity; two revealed a history of nephrolithiasis; and one of these two had a member who received liver and kidney transplants because of primary hyperoxaluria type I. All the patients presented with the symptoms and findings of acute renal failure. Their hemoglobin levels were between 6.8-9.6 g/dl, urinalysis revealed (+) to ( +) proteinuria and microscopic hematuria. All had metabolic acidosis with BUN levels 67-113 mg/dl and creatinine 3.5-7.7 mg/dl. The abdominal ultrasonographies revealed normal sized hyperechogenic kidneys with the loss of corticomedullary junctions. Calcium oxalate crystals were demonstrated in retina and bone marrow of two patients, and in renal parenchyma of all the patients. The patients were treated with peritoneal dialysis. Renal functions continued to be abnormal (BUN: 47-168 mg/dl, creatinine: 2.8-11 mg/dl) after dialysis, and the outcome was fatal in all. In the presented families, because of the variation of the clinical presentation and the fatal outcome, presence of the multiple genetic loci appeared to be most likely. Further molecular studies will clarify the heterogeneity of this disorder.