The incidence and prevalence of Actinobacillus actinomycetemcomitans, Porphyronmonas gingivalis, and Tannerella forsythensis in specimens of subgingival dental deposit were evaluated in 495 residents of St. Petersburg aged 6-82 years. The microorganisms were detected by gene-specific PCR of 16S rDNA. In accordance with age-specific increase in the incidence of gingival diseases, the percentage of samples containing T. forsythensis and P. gingivalis was significantly higher in adult and elderly patients in comparison with adolescents. The presence of T. forsythensis significantly correlated with the presence of gingivitis and dental deposit. In addition, the incidence of T. forsythensis was significantly higher in tobacco smokers. These results attest to a relationship between T. forsythensis infection and more frequent periodontal diseases associated with aging and tobacco smoking.