We examined the records of patients with hemolytic uremic syndrome, who had not undergone dialysis during the acute stage, with the aims of evaluating: (1) the outcome after at least 5 years of follow-up; (2) the value of peak serum creatinine as a prognostic marker; (3) the relationship between outcome and time to normalization of renal function. From 1968 to 2000, 1,179 patients were assisted. Forty-two patients (3.6%) died during the acute stage, 478 patients (40.5%) required dialysis and 659 patients (55.9%) did not undergo dialysis; 529 non-dialysis patients were lost to follow-up. The remaining 130 patients were classified into four groups: group I, complete recovery; group II, with two subgroups, IIa, microalbuminuria, and IIb, proteinuria and/or high blood pressure, both with normal renal function; group III, chronic renal failure; and group IV, end-stage renal disease. We analyzed the relationship between final outcome and: (1) peak creatinine (the highest of at least two determinations) during the acute stage and (2) time to normalization of urea and/or creatinine after the acute stage. After a mean follow-up time of 147.1 months (range 60-362 months), group I had 83 patients (63.9%), group IIa had 27 (20.8%), group IIb had 15 (11.5%) and group III had 5 (3.8%). The value of peak serum creatinine concentration was available for 57 patients. On the last clinical visit, eight out of 26 (30.7%) patients with peak serum creatinine equal to or higher than 1.5 mg/dl were in groups IIb and III versus one out of 31 (3.2%) patients with lower values (P < or = 0.007). Finally, six out of 28 patients (21%) whose renal function had normalized after 15 days from diagnosis were in groups IIb-III versus 8/82 (9.7%) whose renal function had normalized within 15 days (P = 0.18). After a mean period of follow-up of 12 years, 15% of a selected patient group had developed proteinuria, high blood pressure or chronic renal failure, and 21% had developed microalbuminuria. Peak serum creatinine during the acute stage was useful as a prognostic indicator. Patients whose renal function required more time to normalize did not have a worse outcome.