There are few reports of IgG4-related vascular lesions involving arteries other than the aorta, and there are some cases in which imaging and pathological examinations did not show a typical picture. In this report, a case of an IgG4-related femoral aneurysm is described. The patient was a man in his 70s who was diagnosed with an aortic arch aortic aneurysm, a superior mesenteric aneurysm, bilateral common iliac aneurysms, and bilateral femoral aneurysms by a previous physician 7 years before his first visit to our department. Four years earlier, a previous doctor performed a prosthetic vascular replacement of the aortic arch to enlarge the diameter of the arch lesion. Computed tomography 4 years after surgery showed enlargement of the diameter of the right femoral aneurysm, and he was referred to our department. Immunological tests were performed for vasculitis, and IgG4 was high (702 mg/dL). Prosthetic vascular replacement of the aneurysm was performed, and a collection of IgG4-positive plasma cells was found in the aneurysm wall, leading to the diagnosis of IgG4-related vascular lesions. Surgical treatment was performed to prevent rupture, but there are reports that steroids suppress the expansion of blood vessel diameter in this disease, and it is necessary to carefully consider the possibility of medical treatment with early diagnosis.