A working classification of necrotizing vasculitis based on size of the affected vessel is proposed. The classification proposed by Gilliam and Fink in 1976 is a basis for the current proposal. A revised working classification of vasculitis is presented. Small vessel necrotizing vasculitis and larger vessel necrotizing vasculitis categories are further subdivided. Improved understanding of the basic science aspects of vasculitis will hopefully give rise to a better consensus on the classification of vasculitis.