**1. Introduction**

Several previous studies have demonstrated a possible association between the infection by *Chlamydia pneumoniae* and atherosclerosis and stroke. The demonstration of the presence of the pathogen in the atherosclerotic parts of the infarctrelated arteries and the increased Chlamydia pneumonia antibody titers in stroke patients raises suspicions about the role of Chlamydia pneumonia infections in development of stroke. Besides these, several animal and *in vitro* studies support the hypothesis that Chlamydia pneumonia has role in atherosclerosis development, and its complications resulting in the stroke. In this chapter, we will summarize the epidemiology, pathophysiology, and its associations with the infections and the possible pathophysiological mechanisms of the Chlamydia pneumonia in the

development of atherosclerosis and atherosclerosis-related complications resulting in the cerebral infarcts.
