Objectives: The frequency of gingival and periodontal disease in HIV-seropositive and AIDS patients was investigated in order to evaluate the oral hygiene benefits of using mechanical therapy. Study design: thirty-two consenting HIV-positive patients were examined. Their gingival and periodontal status were evaluated using the Gingival Index and the Simplified Oral Hygiene Index. The data were assessed at baseline, after three months and after six months. Subjects received mechanical therapy, which included calculus removal, scaling and root planning, tooth polishing and oral hygiene instructions. The maintenance of oral hygiene was performed weekly. HIV staging and CD4 counts were also investigated. Results: At the baseline, gingival and periodontal disease was present in 71.9% of all subjects. Chronic gingivitis (43.8%) was the most frequent in all subjects. A clear improvement in gingival health was registered in 78.2% of subjects after six months of mechanical therapy. No association was registered between CD4 count and gingival/periodontal status or attachment loss with HIV staging. Conclusions: Chronic gingivitis was the most frequent disease in HIV infected and AIDS patients. Oral hygiene using mechanical therapy improves the gingival condition, suggesting that it is an important step in the maintenance of periodontal health.