Antineutrophil Cytoplasmic Autoantibody-Associated Glomerulonephritis; This is a literature report.  The authors report here a case of pauci-immune crescentic glomerulonephritis associated with Regulatory Authority following vaccination with the Pfizer- BioNTech COVID-19 vaccine. A 29-year-old woman was referred for evaluation of acute kidney injury. She had a history significant for congenital diffuse cystic lung disease, attributed to a mutation in the surfactant SFTPC gene. She had progressive lung failure complicated by pulmonary hypertension and was on the waitlist for a lung transplant. Her medications included tadalafil, macitentan, and escitalopram. She had chronic dyspnea and dry cough, which were stable over the preceding 6 months. Her review of systems was otherwise negative, and she reported no symptoms suggestive of infection in the past year or recent change in medications. On examination, her blood pressure was 117/81 mm Hg, her lungs had bilateral crackles (chronic), and there was no edema and no neurologic or skin findings. Her baseline creatinine was 0.8 mg/dl 1 week prior to receiving her first dose of the Pfizer-BioNTech COVID-19 vaccine. Sixteen days after receiving her second vaccine dose, her creatinine had increased to 1.25 on routine laboratory tests. Routine laboratory tests 7 weeks after her second dose of vaccine showed a creatinine of 1.91 mg/dl. Further evaluation showed the following: urine with 12 red blood cells / high-power field; urine albumin-creatinine ratio 633 mg/ mg; serum albumin 4.4 g/dl; C3 108 mg/dl; C4 29 mg/dl; negative serologic test results for hepatitis B, hepatitis C, and HIV; negative test results for antiglomerular basement antibody and proteinase 3 (PR3)-ANCA; and a positive test result for myeloperoxidase (MPO)-ANCA at 71 AU (arbitrary units)/ml. Test results for ANCA 2 years earlier was negative. Screening test results for SARSCoV- 2 were negative 2 months before the first dose of vaccine and 3 weeks after the second dose of vaccine. A percutaneous kidney biopsy was performed 9 weeks after the second vaccine dose. The light microscopy sample contained 44 glomeruli, of which 8 were globally sclerotic. Of the 36 nonglobally sclerotic glomeruli, 9 showed cellular crescents, 5 displayed fibrocellular crescents, and 7 exhibited fibrous crescents. The remaining glomeruli appeared of normal size without significant mesangial proliferation, mesangial sclerosis, or endocapillary proliferation. These findings were accompanied by mild diffuse mononuclear interstitial inflammation, foci of moderate tubulitis, and scattered red blood cell casts. These changes were superimposed on 40% tubulointerstitial scarring and mild vascular sclerosis. Except for fibrin staining in Bowman space in 4 of the 7 sampled glomeruli, which was consistent with crescents, the remaining immunofluorescence findings were essentially unremarkable. Electron microscopic evaluation revealed focal foot process effacement without discrete electron-dense deposits. Taken together, the above findings were consistent with pauci-immune crescentic glomerulonephritis, correlating with her positive MPO-ANCA serologies. Based on the results of her biopsy, she was started on treatment for her ANCA-associated glomerulonephritis with steroids (methylprednisolone 500 mg daily for 3 doses, followed by prednisone 1 mg/kg daily), rituximab (1000 mg for 2 doses, spaced 2 weeks apart), and intravenous cyclophosphamide (500 mg for 2 doses, spaced 2 weeks apart). At last follow-up, 10 weeks after her biopsy, her creatinine was 1.01 mg/dl, her albumin-creatinine ratio was 1393 mg/mg, her urine showed 0 to 2 red blood cells / high-power field, and her MPO-ANCA titer was negative. Hundreds of millions of doses of COVID-19 vaccines have been administered worldwide, with rare autoimmune side effects reported to date. In this case, ANCA and ANCA-associated glomerulonephritis developed shortly after receiving the COVID-19 vaccine, in the absence of any recent infection or medication use known to trigger ANCA development. Although causality can be difficult to establish, the development of ANCA and ANCA-associated vasculitis after both natural SARS-CoV-2 infection and following other vaccinations lends support to the authors' hypothesis that the ANCA-associated vasculitis in this case is related to the recent Pfizer-BioNTech COVID-19 vaccine.; Sender's Comments: Based on the information currently available, a possible contributory role of the suspect drug in the reported serious event cannot be completely ruled out given the known suspect drug profile and/or implied temporal association. The impact of this report on the benefit/risk profile of the Pfizer product is evaluated as part of Pfizer procedures for safety evaluation, including the review and analysis of aggregate data for adverse events. Any safety concern identified as part of this review, as well as any appropriate action in response, will be promptly notified to Regulatory Authorities, Ethics Committees and Investigators, as appropriate.