About 25-50% of survivors of the acute phase of postdiarrheal hemolytic uremic syndrome (D+ HUS) develop chronic renal disease. Transforming growth factor beta-1 (TGFbeta-1) is the main fibrogenic growth factor in humans, and there is a significant correlation between its levels and the grade of interstitial fibrosis in chronic nephropathies. We hypothesized that increased urinary TGFbeta-1 may be an early indicator of sequelae in D+ HUS patients who show no sign of renal damage as determined by conventional diagnostic tests. We therefore compared the levels of TGFbeta-1 in urine collected from healthy controls (HC) (n = 18) with that from patients with a past history of D+ HUS (n = 39). We found that TGFbeta-1 excretion was significantly higher (p < 0.001) in the patient group (median level 73 pg/mg creatinine) than in the HC (median level 28 pg/mg creatinine). TGFbeta-1 excretion did not correlate with age, white blood cell count, length of oligoanuric period, maximum creatinine at the acute stage, or length of the follow-up. Since TGFbeta-1 excretion may reflect ongoing renal tissue damage, our results emphasize the need for the lifelong follow-up of patients with a past history of D+ HUS, even those showing apparent recovery. Long-term monitoring of this cohort is necessary to determine the clinical utility of our findings.