BACKGROUND AND OBJECTIVE Weak oral bacteria, such as periodontal bacteria, have been found in various vascular lesions, including atheroma, the thrombus of the occluded artery of Buerger's disease, the abdominal aortic aneurismal wall and varicose veins. Serum titer levels of each bacterium are now available and have shown a significant relationship between severity and individual differences. MATERIAL AND METHODS The Medline and Tokyo Medical and Dental University databases were searched to identify the literature currently available on oral bacteria and vascular diseases. RESULTS It is estimated that lymph vessel openings trap bacteria en route from the mouth to the bloodstream and then carry them to the vein of the venous angle near the supraclavicular area. In the case of periodontal bacteria, a typical bacterium, such as Porphyromonas gingivalis, strongly activates platelets and makes them mass, including the bacteria without phagocytosis. Simultaneously, cytokines and serotonin are discharged. Platelet engulfment was clearly demonstrated by electron microscopy analysis. An animal study using rats showed the formation of a small arterial thrombus after continuous intravenous infusion of P. gingivalis for 2-4 wk. CONCLUSION Weak oral bacteria, such as periodontal bacteria, may play an important role in the development of various vascular diseases, such as Buerger's disease, atherosclerosis and varicose veins, through bacteremia.