Acute renal failure that is associated with macroscopic hematuria (ARF-MH) is a widely known complication of IgA nephropathy (IgAN). Although spontaneous recovery of renal function after cessation of MH has been described, no long-term outcome studies have been performed. The outcome of patients who had biopsy-proven IgAN and presented an ARF-MH episode in the period 1975 through 2005 was studied. Thirty-six episodes of ARF-MH that occurred in 32 patients were identified. A complete recovery of baseline renal function after cessation of MH was observed in 27 (group 1); in the remaining nine episodes (25%; group 2), estimated GFR (eGFR) did not reach the baseline value. Final eGFR was 89 +/- 28 ml/min per 1.73 m(2) in group 1 patients and 38 +/- 12 ml/min per 1.73 m(2) in group 2 patients (P = 0.0005). The duration of MH was significantly longer in group 2 patients: 33.7 +/- 25.3 versus 15.4 +/- 18.4 d (P = 0008). A high proportion of tubules that were filled by red blood cell casts and had signs of acute tubular necrosis were the most striking histologic abnormalities. In conclusion, a significant proportion (25%) of ARF-MH in IgAN did not recover the baseline renal function after the disappearance of MH. Duration of MH longer than 10 d, age >50 yr, decreased baseline eGFR, absence of previous episodes of MH, and the severity of tubular necrosis were significant risk factors for an incomplete recovery of renal function.