Vasculitis is defined as angiocentric segmental inflammation of the blood vessels and fibrinoid necrosis of the vessel wall. Classification of vasculitis is a controversial problem, because of the difficulty in incorporating globally different criteria such as histologic features, size of affected blood vessels, etiology, pathogenesis and other factors in a single classification schema. In this paper we review the principal classifications and make a novel attempt to classify vasculitis on the basis of the size of affected vessels. We hope that a new generation of basic and clinical investigators can achieve a better understanding of the pathogenesis of various vasculitis-related syndromes and that this understanding will facilitate future classification schemas.