Short-term prognosis of rapidly progressive glomerulonephritis (RPGN) has improved since immunosuppressive therapy was introduced. The long-term course of the disease was investigated in 46 consecutive and unselected patients over a period of 15 years (1970-1986) with a mean observation time of five years (+/- 45 months). Most of the 46 patients had idiopathic RPGN (61%). Initially, hemodialysis needed 25 of the 46 patients (54%). Immunosuppressive therapy (plasma exchange, methylprednisolone pulses, steroids, cyclophosphamide, azathioprine) was administered in 36 of the 46 patients (78%). A remission was achieved in only 19 of the 36 patients who received immunosuppression (53%) and no spontaneous improvement was seen. Factors indicating poor prognosis were initial high serum creatinine, high percentage of crescents in glomeruli, glomerular sclerosis, and immunohistologic staining of the IgG at the tubuli. In 11 patients with remission, immunosuppression was discontinued and 6 had a relapse. Long-term immunosuppression was given to 8 patients with remission. Their renal function was not normal (creatinine 240 +/- 77 mumol/l), but none had a relapse (p = 0.01). It is concluded that the treatment of RPGN requires long-term attendance and repeated immunosuppression comparable to a systemic immune disease.