Microorganisms have evolved a variety of mechanisms designed to evade detection and/or destruction by the host. Many pathogens evade host defenses by invading cells, thus providing the bacterium with an environment free of competing microorganisms. Adherence and invasion are active processes in which microorganisms often use host proteins and enzymes to gain entry into the cell, thus stimulating their own uptake. The investigation of invasion by the periopathogen Porphyromonas gingivalis is in its infancy in comparison with that of the enteric pathogens. However, recent studies with P. gingivalis have revealed that these organisms have developed invasion strategies and mechanisms similar to those of the enteric pathogens for both epithelial and endothelial cells. The study and elucidation of the mechanisms by which microorganisms such as P. gingivalis persist in chronic infection will provide valuable insight into the pathogenesis of P. gingivalis-mediated periodontal disease. The ability to multiply in and to activate endothelial cells may be one of the pathogenic mechanisms exerted by P. gingivalis that may explain the recently described association between this organism and cardiovascular disease.