Periodontitis is a chronic infectious disease, characterized by the progressive loss of the teeth's supporting tissues, affecting almost 40% of the entire adult population. An imbalance between a localized gram-negative infection and an exaggerated host inflammatory response plays a pivotal role in determining gingival tissue damage. Recent evidence suggests that the effect of periodontitis might not be limited just to the oral cavity but it might have systemic consequences. Indeed periodontitis has also been associated with a moderate systemic inflammatory response. Although the mechanisms behind this association remain unclear, periodontitis might represent one distant source of low-grade systemic inflammation. This association could explain the increased risk of future cardiovascular diseases observed, the impaired metabolic control in diabetes subjects and the adverse pregnancy outcomes observed in populations suffering from periodontitis. In this review we describe the pathophysiological processes involved in periodontitis and briefly review the evidence produced to support an association between periodontitis and systemic diseases.