The aim of our study was to assess the presence of Chlmydia pneumoniae infection in AAA patients and to evaluate its association with clinical symptoms and histological signs of inflammation in the aortal wall. Fifty-two AAA patients participated in the research. Thirty healthy controls took part in serological examination. C. pneumoniae was detected by PCR and immunofluorescence in situ reaction in aorta samples of 84.6% and 86.54% of the patients, respectively. Serological markers of chronic C. pneumoniae infection were detected in 86.5% of AAA patients and in 33.3% of healthy controls. High titers of specific IgG and IgA were found in 37.8% of AAA patients with serologically defined chronic infection. All patients in "high serology" group had symptomatic aneurysm and inflammatory infiltrations in their aortal wall samples. AAA patients infected with C. pneumoniae are not a homogenous group. "High serology" group is much more prone to have symptomatic aneurysm than the remaining of AAA patients. Serology can be very useful in predicting the risk of AAA rupture. Inter-laboratory standardization of direct and indirect detection methods of C. pneumoniae infection is required to elucidate the role of these bacteria in AAA development.