The purpose of this paper is to trace the evolution of AIDS definition and describe the principal classification systems of HIV infection as defined since 1981. Our work is principally based on data from the American Centers of Disease Control on the one hand (clinical evaluation of infection stage) and from the Walter Reed Institute (immunological evaluation of infection stage) on the other hand. To describe this disease with multiple aspects the separate use of these two classification systems does not provide a thorough evaluation of the patient's condition. Non consensus had been reached to date, although an agreement on this matter would foster an important epidemiological and therapeutic progress in both adult and childhood patients.