When putative periodontal bacteria from the mouth and throat are inhaled into the lower respiratory tract, they can cause infection or exacerbate existing conditions, such as chronic obstructive pulmonary disease and emphysema. Literature suggests that patients with periodontal disease have elevated levels of bacteria, including gram-negative enteric species and Pseudomonas aeruginosa. In fact, scientists estimate the prevalence of certain microorganisms - staphylococci, Enterobacteriaceae, and yeasts - in dental plaque to be upwards of 77 percent. Some microorganisms are particularly difficult to eradicate, remaining in patients with periodontal disease even after antibiotic treatment. Any bacterial presence, in turn, places individuals at a higher risk for developing disorders like pneumonia. This life-threatening infection affects patients of all ages, but particularly the elderly and immunocompromised individuals. This article provides the biological basis for the connection between periodontal disease and respiratory disease.