A 62-year-old man with a history of proteinase 3-specific antineutrophil cytoplasmic antibody-associated vasculitis, antiphospholipid syndrome, and deep vein thrombosis presented with an asymptomatic 15-mm-diameter right superficial femoral artery (SFA) aneurysm, showing increased intraluminal thrombus on computed tomography compared to 2 years prior. The gene discussed is PRTN3; the disease is vasculitis.