Rapidly progressive glomerulonephritis (RPGN) is a rare but severe condition, with a particular poor outcome in the absence of aggressive therapy. Our study describes all RPGN consecutive cases treated during the 1994-1995 period, with special interest in revealing negative prognostic features at presentation and the optimum therapeutic strategy. 14 (20% of all ARF for the same period) cases were classified as RPGN. Although rare (30%), extrarenal symptoms were related with a more unfavourable course. Creatinine clearance at presentation was not a reliable prognostic factor in our study. ANCA was found in 86% of our patients (p-ANCA/c-ANCA = 2/1), and therapeutic success was associated with ANCA disappearance. Crescentic glomerulonephritis was seen in 93% of all cases 77% of which were type III, pauciimune, ANCA positive. Vasculitic lesions and fibrous crescents, but not % of glomerular circumference or % of affected glomeruli were also related with a poor prognosis. Only 43% of our RPGN cases survived with a normal renal function. i.v. metil-prednisolone (at presentation, as soon as possible) followed by i.v. cyclophosphamide up to six months was the best therapeutic regimen, with no important side-effects.