Atherosclerosis is caused by multiple factors. Infectious disease has been proposed to be one of the causative factors, and several bacteria and viruses have been studied for their correlations with atherosclerotic diseases; these organisms include Chlamydia pneumoniae, Helicobacter pylori, HIV, CMV, HSV and hepatitis viruses. Many underlying mechanisms that infectious diseases cause atherosclerosis have been proposed; most of them suggested that inflammatory process provoked by infectious diseases led to atherosclerosis. Several clinical studies were also performed to examine whether treatment for infectious diseases could protect against atherosclerosis. However, the relationship between infectious diseases and atherosclerotic diseases and the effects of treatment for infectious diseases on atherosclerosis are still controversial; there are both positive and negative reports. Thus, further studies are needed to clarify the correlation.