When hemolytic uremic syndrome (HUS) is occasionally inherited in an autosomal recessive mode, this occurs mainly in infants and children. We describe four families in which two adult siblings were affected with HUS in each kindred. HUS first occurred between the ages of 19 to 36 years, and the intervals between the onset of HUS in each sibling pair ranged from 6 months to 6 years. None of the patients had a typical prodrome of bloody diarrhea, and one had a recurrence of HUS before transplantation. All eight patients developed renal failure requiring dialysis and transplantation, and seven patients received kidney transplants. Donor kidneys were from parents, siblings, and cadavers. The initial renal transplants were performed from 6 months to 6 years after the onset of the syndrome. HUS recurred in six of the seven patients 2 weeks to 6.5 years after transplantation regardless of the interval between the onset of HUS and transplantation, the origin of the allograft, or the use of cyclosporin A. The only marker for autosomal recessive HUS is the occurrence of the syndrome in a second sibling several months to many years after its occurrence in the proband. In patients with the autosomal recessive form of HUS, the risk for a recurrence in an allograft is high regardless of the source of the kidney.