We retrospectively analyzed the courses of 70 patients with lupus nephritis followed for 5 to 30 years (median 127 months). Patients survival was 100% at 10 years and 86% at 20 years. The probability of not reaching the end point (persistent doubling of plasma creatinine) was 85% at 10 years and 72% at 20 years. A multivariate analysis of variables at presentation showed that male sex (P = 0.005) and hematocrit lower than 36% (P = 0.01) were associated with the end point (relative risk 7.5 and 14). We then analyzed for the role of renal flare-ups, defined either as a rapid increase in plasma creatinine or by an increase in proteinuria. Patients with renal flares of any type had more probabilities of reaching the end point than patients who never had flares (P = 0.03; relative risk 6.8). The hazard of the end point was 27 times higher in patients with flares along with rapid increased in plasma creatinine than in patients without flares or with flares with proteinuria alone (P < 0.00001). This hazard was higher when plasma creatinine did not return to the basal levels within two months after treatment (P < 0.00001).