Anti-neutrophil cytoplasmic antibody (ANCA)-associated systemic vasculitis is reported mainly in adults. Studies in children are limited. The current study retrospectively analyzed the clinical characteristics and pathology of ANCA-associated systemic vasculitis in children in our hospital during the past 7 years. Twenty-four pediatric patients were diagnosed as having ANCA-associated systemic vasculitis, including 19 patients with microscopic polyangiitis (MPA), one with Wegener's granulomatosis (WG), three with propylthiouracil (PTU)-induced ANCA-positive vasculitis and one with anti-glomerular basement membrane (GBM) disease. Of patients with primary ANCA-associated systemic vasculitis (MPA and WG), with an average age of 10.8+/-2.8 (6-14) years, 18 patients (90%) were female and two (10%) were male. Nineteen patients (95%) were p-ANCA/MPO-ANCA positive and one (5%) was c-ANCA/PR3-ANCA positive. The interval between onset and diagnosis was 8.5+/-24.3 (0.2-108) months. The majority of the patients (85%) had multi-organ involvement. All patients had clinical evidence of renal involvement and presented with hematuria and proteinuria. Of 20 patients, 16 (80%) also had acute renal failure, and five patients were dialysis dependent. Nine patients underwent renal biopsy and were diagnosed with necrotizing and crescentic glomerulonephritis. However, six biopsies showed immune complex deposition. All patients received immunosuppressive therapy including prednisone and cyclophosphamide, and ten patients also received intravenous administration of methylprednisone pulse therapy according to their clinical situation and renal pathology. Sixteen patients achieved clinical remission, and four patients presented as treatment failure. Patients were followed up for 12.3+/-5.1 months (median 12 months; range 1 to 91 months). Ten patients maintained their clinical remission, and ten progressed to renal failure requiring dialysis. Our study showed that the clinical features and pathology of primary ANCA-associated systemic vasculitis in children were similar to those of adults, but there were a predominance of female patients and late diagnoses. We suggest that early recognition and prompt aggressive treatment might improve outcome.