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Background There are few anecdotal reports of circulating antineutrophil cytoplasmic autoantibodies (ANCAs) in patients with immunoglobulin A (IgA) nephropathy. Study Design Retrospective case series. Setting & Participants We studied 8 patients with crescentic IgA nephropathy associated with ANCAs against myeloperoxidase (n = 5) and proteinase 3 (n = 3) followed up for 2.4 ± 1.7 years. They were compared with 26 patients with IgA nephropathy with > 10% crescentic glomeruli, but negative for ANCAs. Outcomes We analyzed clinical and histologic features of patients and their response to treatment. Measurements Screening for ANCAs was performed using indirect immunofluorescence, and positive results were verified using enzyme-linked immunosorbent assay. Results All patients with crescentic IgA nephropathy and positive for ANCAs, compared with only one-third of ANCA-negative patients, presented with the clinical syndrome of rapid progressive glomerulonephritis. ANCA-positive patients reached a higher peak serum creatinine level within the first 3 months (4.2 ± 2.2 vs 2.5 ± 1.9 mg/dL; estimated glomerular filtration rate, 19.3 ± 10.2 vs 45.9 ± 30.1 mL/min/1.73 m 2 ). ANCA-positive patients with IgA nephropathy had a higher percentage of crescentic glomeruli (54.3% ± 18%) compared with ANCA-negative patients with crescentic IgA nephropathy (34.5% ± 26%). ANCA-positive patients were treated using cyclophosphamide and corticosteroids. Kidney function improved in all these patients: serum creatinine level decreased from the peak of 4.2 ± 2.2 to 1.7 ± 0.7 mg/dL at the end of follow up (estimated glomerular filtration rate, 19.3 ± 10.2 to 44.6 ± 11.1 mL/min/1.73 m 2 ). In contrast, no significant improvement was achieved in ANCA-negative patients. Conclusion Patients with IgA nephropathy, crescents, and positive for ANCAs represent a clinical entity with a diverse more exaggerated clinical and histologic picture. However, disease in these patients responded well to aggressive immunosuppressive therapy.