OBJECTIVES: To identify predictors of complete renal response (CRR) and renal flares in SLE patients with active proliferative LN. METHODS: This was a retrospective cohort study over 36 months including patients with biopsy-proven proliferative LN (class III/IV), from two European tertiary centres. CRR and renal flare were defined as proteinuria <0.5 g/day with normal renal function and proteinuria >1 g/day after CRR attainment, respectively. Demographic, clinical and analytic parameters were evaluated as early predictors of renal outcome, using survival analysis. Candidate variables were tested as predictors for CRR at time 0, 3 and 6 months after starting induction treatment. Potential predictors for renal flare were evaluated at time of reaching CRR. Variables with P < 0.10 on univariate analysis with log-rank tests were further tested with multivariate Cox proportional hazards regression models. RESULTS: We included 104 patients [81.7% female, mean (s.d.) age at baseline 32.0 (13.3) years]. Over follow-up, 91.7% reached CRR, within a median time of 6.0 months. Proteinuria <2 g/day at baseline [hazard ratio (HR) = 1.80, 95% CI 1.16, 2.79, P < 0.01] and 3 months (HR = 2.32, 95% CI 1.24, 4.32, P < 0.01) after starting induction therapy were independent predictors of CRR. Renal flares occurred in 18.4% of patients reaching CRR, after a mean time of 16.5 (8.6) months. Age up to 25 years at time of LN diagnosis (HR = 5.41, 95% CI 1.72, 16.97, P < 0.01) and positive anti-RNP (HR = 3.52, 95% CI 1.21, 10.20, P = 0.02) were independent predictors of renal flares. CONCLUSION: In patients with SLE and proliferative LN, factors assessed at baseline and 3 months from starting induction treatment can predict CRR and renal flares once CRR is achieved.