The incidence of renal flares and the long-term outcome in a group of 33 systemic lupus erythematosus (SLE) patients with diffuse proliferative glomerulonephritis (DPGN) treated with pulse steroids and a short course of pulse cyclophosphamide (CYC) are evaluated. Fifteen patients (45%) experienced a flare of renal disease at some time after the discontinuation of the immunosuppressive (IS) therapy; among these half (24%) were 'early' flares occurring shortly after the discontinuation of therapy, and the other half (21%) were 'late' flares occurring more than 2 y after the discontinuation of the treatment. Nine patients (27%) showed a poor renal outcome at the end of follow-up. On multiple regression analysis, a younger age and a high activity index (AI) on renal histology were found to be correlated with the occurrence of renal flares. Our results suggest that the combination of pulse steroids with a short course of pulse CYC (six to nine pulses) is effective in both controlling disease activity and in preventing the occurrence of renal flares in DPGN. However, short term IS therapy might not be sufficient to maintain disease control in younger patients with active lesions on renal histology. Such patients might be candidates to receive more prolonged IS treatment.