The aim of this study was to describe the clinical characteristics of ANCA-associated vasculitides (AAV) at presentation, in a wide cohort of Spanish patients, and to analyze the impact of the vasculitis type, ANCA specificity, prognostic factors, and treatments administered at diagnosis, in the outcome.A total of 450 patients diagnosed between January 1990 and January 2014 in 20 Hospitals from Spain were included. Altogether, 40.9% had granulomatosis with polyangiitis (GPA), 37.1% microscopic polyangiitis (MPA), and 22% eosinophilic granulomatosis with polyangiitis (EGPA). The mean age at diagnosis was 55.6 ± 17.3 years, patients with MPA being significantly older (P < 0.001). Fever, arthralgia, weight loss, respiratory, and ear-nose-throat (ENT) symptoms, were the most common at disease onset. ANCAs tested positive in 86.4% of cases: 36.2% C-ANCA-PR3 and 50.2% P-ANCA-MPO. P-ANCA-MPO was significantly associated with an increased risk for renal disease (OR 2.6, P < 0.001) and alveolar hemorrhage (OR 2, P = 0.010), while C-ANCA-PR3 was significantly associated with an increased risk for ENT (OR 3.4, P < 0.001) and ocular involvement (OR 2.3, P = 0.002). All patients received corticosteroids (CS) and 74.9% cyclophosphamide (CYC). The median follow-up was 82 months (IQR 100.4). Over this period 39.9% of patients suffered bacterial infections and 14.6% opportunistic infections, both being most prevalent in patients with high-cumulated doses of CYC and CS (P < 0.001). Relapses were recorded in 36.4% of cases with a mean rate of 2.5 ± 2.3, and were more frequent in patients with C-ANCA-PR3 (P = 0.012). The initial disease severity was significantly associated with mortality but not with the occurrence of relapses. One hundred twenty-nine (28.7%) patients (74 MPA, 41 GPA, 14 EGPA) died. The mean survival was 58 months (IQR 105) and was significantly lower for patients with MPA (P < 0.001). Factors independently related to death were renal involvement (P = 0.010), cardiac failure (P = 0.029) and age over 65 years old (P < 0.001) at disease onset, and bacterial infections (P < 0.001). An improved outcome with significant decrease in mortality and treatment-related morbidity was observed in patients diagnosed after 2000, and was related to the implementation of less toxic regimens adapted to the disease activity and stage, and a drastic reduction in the cumulated CYC and CS dose.