The occurrence of unusual and severe forms of periodontal disease in HIV-infected individuals is well recognised. Several classification schemes have been proposed in an effort to associate periodontal deterioration with progressive stages of HIV infection and to determine aetiological factors in tissue destruction. No classification to date has proved entirely satisfactory. This paper reviews current classification schemes and suggests an alternative based upon the periodontal status of a cohort of HIV seropositive patients in Edinburgh. The proposed classification includes 'conventional', non-specific gingivitis and adult periodontitis such as occur in HIV seronegative individuals, but which may also be seen in seropositive subjects. However, conditions termed linear gingivitis and necrotising periodontitis may be pathognomonic for HIV infection. It is recommended that the term 'HIV-associated' be dropped in relation to periodontal disease.