Small vessel vasculitides, usually associated with positive antineutrophil cytoplasmic antibodies (ANCA(+)) can cause pulmonary-renal syndrome (PRS). Data from 22 patients, (19 males), aged 28-76 yrs (mean 55), with PRS were analyzed retrospectively. Renal function was estimated at presentation, 1 month after treatment initiation and at the end of follow-up (mean 4.4 +/- 3.3 yrs). Thirteen out of 22 patients had PR3 (+) ANCA and 9/22 patients had MPO (+) ANCA. Mean serum creatinine (Cr) at diagnosis was 6.6 +/- 4.4 mg/dL (M +/- SD) and proteinuria 1.6 +/- 1.4 g/24 hr (M +/- SD). During the 1st month of treatment with corticosteroids and cyclophosphamide, renal function improved in 12 patients (54.5%) (serum Cr from 8.5 +/- 4.5 to 4.3 +/- 2.3 mg/dL, p=0.001) remaining stable thereafter, and renal function deteriorated in nine patients (41%) (serum Cr from 4.1 +/- 3 to 6.5 +/- 2.9 mg/dL, p=0.03); one patient (4.5%) died because of sepsis. At the end of the study, 11/22 patients (50%) had died, eight patients of these (73%) because of respiratory failure, three patients (13.6%) reached end-stage renal disease (ESRD), five patients (36.4%) remained stable, but with impaired renal function and finally three patients (13.6%) improved, achieving almost normal renal function. In multiple regression analysis, factors contributing to final serum Cr were: dialysis dependency at the time of diagnosis p=0.01, initial proteinuria p<0.0001, and percentage of cellular crescents p=0.003. Main differences between PR3 and MPO (+) patients were the chest CT findings (bilateral nodules in PR3 (+) and "ground glass" or fibrosis in MPO (+) patients) and the renal function improvement rate after treatment initiation (rapid decline in serum Cr in PR3 (+) patients). In conclusion, PRS with ANCA (+) is associated with increased mortality. If renal function improves during the 1st month of treatment, it usually remains stable thereafter. The presence of PR3-ANCA is associated with an early response to treatment, while MPO-ANCA vasculits seems to necessitate prolonged treatment.