Granulomatosis with polyangiitis (GPA) is the name that has been used in recent years for Wegener's granulomatosis. This condition is a systemic inflammatory disease characterised by necrotizing vasculitis that affects small and medium-sized blood vessels (capillaries, arterioles, venules and arteries). The granulomatous inflammation affects the respiratory system; it also commonly affects the kidney and can very rarely affect large vessels such as the aorta and the surrounding retroperitoneal tissue. Early diagnosis and treatment is of vital importance because of the high risk of dissection and of obstruction of retroperitoneal structures. We present the case of a 74-year-old man with a past history of infrarenal abdominal aortic aneurysm. He consulted for abdominal pain. Cavitating pulmonary nodules and retroperitoneal fibrosis with periaortic alterations were detected on computed tomography. Laboratory investigations revealed that the patient was positive for cytoplasmic antineutrophil cytoplasmic antibodies (c-ANCA) and necrotizing granulomas were observed on biopsies of the lung lesions and retroperitoneal tissue. The patient was diagnosed with GPA and treatment was started with glucocorticoids and immunosuppressive agents, which led to a significant clinical and radiological improvement over the following months.