Systemic vasculitis is a clinical and pathological process characterized by inflammation and damage to blood vessels. Within the entire spectrum of vasculitis virtually any size or type of blood vessel in any organ system can be involved. Vasculitis may be the primary feature of the disease or may accompany or complicate other connective tissue diseases.Immunopathogenic mechanisms are thought to be implicated in most vasculitides. In recent years several of the serious vasculitides, such as Wegener's granulomatosis and polyarteritis nodosa, which previously had a poor prognosis, have now been shown to be responsive to cytotoxic therapy, particularly to treatment with cyclophosphamide.