Aortitis may result in an injury to the aorta or its branches. The inflammatory process that occurs in response to the injury may ultimately result in stenosis or occlusion from fibrosis and dilatation or aneurysm formation from destruction and weakening of the arterial wall. As a result of antibiotics, some diseases known to cause arteritis have declined over the years (most notably syphilis and rheumatic fever). Other systemic diseases not initially thought to have vascular involvement have also been found to be associated with widespread arteritis. All forms of this entity are capable of producing dilatation or aneurysm formation, but only Takayasu's arteritis can produce narrowing or occlusion of the aorta or its branches, with the rare exception of stenosing arteritis, which sometimes follows radiation therapy in childhood. In Takayasu's arteritis, any segment of the aorta, as well as the pulmonary arteries, may be affected. This disease is divided into four types, depending on the location and extent of the arteritis. In Type I, the disease is limited to the aortic arch and its branches. In Type II, the vascular lesions are confined to the descending thoracic and abdominal aorta without involvement of the aortic arch. Type III is mixed, containing features of Types I and II. Type IV is characterized by dilatation and aneurysm formation in the affected vessels and may have pulmonary artery involvement. The four types are described, with their clinical manifestations, diagnosis, and surgical treatment.