The role of various microorganisms including Chlamydophila (formerly Chlamydia) pneumoniae, have been frequently investigated in the pathogenesis of atherosclerosis. In our study, the relationship between C.pneumoniae seropositivity and risk factors for atherosclerosis have been evaluated. A total of 90 atherosclerotic patients (71 of them were male; age range: 45-87 years; mean age: 65.3 +/- 8.7 years) and 90 control subjects without coronary diseases (41 of them were male; age range: 42-84 years; mean age: 61.6 +/- 9.6 years) were included in the study. Both groups were also evaluated for the presence of risk factors such as age, gender, smoking, hypertension, diabetes, obesity, dyslipidemia, familial history and the high levels of ferritin, cholesterol (total, HDL and LDL) and HS (high sensitive)-CRP. The presence of C.pneumoniae IgG, IgM and IgA antibodies were investigated by micro-immunofluorescence (MIF) and ELISA methods using commercial kits (Euroimmun, Germany). The total antibody seropositivity rate was found 100% (90/90) in patient group by both MIF and ELISA methods, while this rate in control group was 94% (85/90) by MIF and 92% (83/90) by ELISA. When MIF test results were taken into consideration (since it is accepted as the reference method for C.pneumoniae serology), IgG, IgM and IgA positivity rates in patient and control groups were found as 100% (90/90) and 89% (80/90); 70% (63/90) and 59% (53/90); 3% (3/90) and 2% (2/90), respectively. Statistically (s)ignificant difference between patient and control groups was detected only for IgG positivity (p < 0.05) and for total antibody positivities (100% and 94%, respectively) (p < 0.05). The evaluation of the risk factors revealed that age, hypertension, dyslipidemia and HS-CRP levels exhibited statistically significant differences between patient and control groups (p < 0.05 for each parameter tested). Statistically significant relation was detected only between high HS-CRP levels and C.pneumoniae seropositivity (p < 0.05). It was concluded that in areas with high C.pneumoniae infection prevalence, early diagnosis and specific treatment of C.pneumoniae infections, may prevent establishment of chronic infection and eliminate a risk factor for the development of atherosclerosis.