This study examines the clinical aspects of HIV-associated periodontal lesions and the prevalence of periodontal pathogens. Subgingival plaque samples were taken from 55 subjects in six study groups: 1) HIV-seropositive patients with gingivitis, 2) necrotizing gingivitis, 3) periodontitis or 4) with health periodontium, 5) patients with rapidly progressive periodontitis or 6) periodontally healthy in whom there was no evidence of HIV infection. Among HIV-positive patients there was a majority (66%) of intravenous drug users. We detected more Bacteroides intermedius, B. buccae and B. oralis in HIV-infected patients with periodontal lesions and in HIV-negative subjects with rapidly progressive periodontitis than in the other groups. High levels of Spirochetes were recovered in both HIV associated necrotizing gingivitis and periodontitis. The results indicate that there is a similarity in the microbiological profile of HIV-associated gingivitis, necrotizing gingivitis, periodontitis and rapidly progressive periodontitis of HIV-negative subjects although significant differences in the clinical aspects of the lesions and in the immune status of the host have been observed.