Hemolytic uremic syndrome is characterized by the simultaneous occurrence of hemolytic anemia, thrombocytopenia, and renal failure. Clinical/ pathologic data, along with the treatment and outcome of 8 adult patients with HUS, are described. There were 7 females and 1 male, age 30.7 +/- 12 years; 7 were White and 1 Black. Three patients were kidney graft recipients, 2 of whom were receiving cyclosporine; 2 patients were postpartum; 1 case followed an abortion; 1 occurred with prodromic infection; and 1 case was without a causal factor. All patients presented with hematuria and 6 with oligoanuria. Laboratory data showed hemolytic anemia with schistocytes, LDH values were 2584 +/- 2191 U/L, platelets were 79,000 +/- 40,000/mL, creatinine concentrations were 5.9 +/- 2.5 mg/dL. Renal biopsy showed thrombotic microangiopathy. Two had predominant glomerular involvement. 2 showed renal cortical necrosis, 4 were marked by predominant arteriolar involvement. In 5 patients dialytic therapy was performed. All were treated with fresh-frozen plasma infusion and 6 with plasmapheresis. Three patients died, 2 without recovery of renal function. In conclusion, the trigger events were related to renal transplant in 3.2 of them taking cyclosporine; 3 with pregnancy; 1 to precedent infection; and 1 with no causal factor. There was no correlation between histological form and outcome in this group of patients. The benefit of plasmapheresis was evident in the recovery of the extrarenal manifestations, although it did not change the renal outcome. The prognosis is poor, with a high mortality (37.5%) and/or end-stage renal failure (37.5%). Complete recovery of renal function was obtained in 25%.