OBJECTIVE: To determine survival, organ damage and predictors of these outcomes in a population-based, longitudinal cohort study of patients with Wegener's granulomatosis (WG). METHODS: In a retrospective study, 56 WG patients (median age 50 yr) were followed for 56.5 months. Clinical and laboratory data, disease activity, organ involvement and the Vasculitis Damage Index (VDI) were recorded at baseline (start of treatment) and at a research visit after 42.5 months. The Kaplan-Meier method was used to estimate survival and Cox proportional hazards and linear regression models were used to study predictors of outcome. RESULTS: Duration of symptoms before the start of treatment (baseline) was 6 months (1-102 months) and 21 patients (37.5%) had organ damage (VDI > or = 1) at baseline. Baseline organ damage was associated with delay in the start of treatment and an elevated serum creatinine concentration. Fifty-five patients received prednisolone (Pred) and 53 patients received cyclophosphamide by intravenous pulse (CYCiv) or as a daily oral dose (CYCpo). CYCiv patients received lower cumulative doses of CYC and spent less time on Pred >20 mg/day than CYCpo patients. Thirteen patients died during the study period. Ten-year patient survival was 75%. Baseline predictors of reduced survival were higher age, dialysis-dependence and the presence of organ damage. Chronic, end-stage renal failure developed in 10 patients overall and was associated with reduced renal function at baseline. Severe organ damage (VDI > or = 5) developed in 71% of the patients and new damage occurred mainly during the first 6 months. Increased time (months) on Pred >20 mg/day during follow-up increased the last VDI [beta=0.5, 95% confidence interval (CI) 0.3 to 0.8], P<0.001), whereas increased time on CYC during the first 6 months reduced the last VDI (beta=-0.6, 95% CI -1.1 to -0.02, P=0.04). CONCLUSION: Treatment with CYC and corticosteroid led to a 10-yr survival rate of 75% in WG but did not prevent severe organ damage. The presence of baseline organ damage was a marker of poor outcome. There was an association between damage and treatment given.