Atherosclerosis is a multifactor disease. Lately, infectious factors such as C. pneumoniae have been found to be involved. To determine whether the infection by C. pneumoniae is a risk factor for atherosclerosis in patients with AIDS. Case-control study on 43 patients with AIDS under HAART (16 cases and 27 controls). To document atherosclerosis, a carotid and transcranial Doppler ultrasound was performed. Anti-C pneumoniae antibodies were searched using a microimmunofluorescence test for IgM and IgG levels. To study the associations with risk of atherosclerosis, Odds Ratios were calculated for each IgG anti-C. pneumoniae antibody titre. A titre of 1:64 significantly increased the risk of atherosclerosis. These results suggest that hypertriglyceridemia and C. pneumoniae infection coexistence significantly increases the risk of atherosclerosis. The inverse geometric average of the antibodies titre against C. pneumoniae in individuals with atheromatous plaque fell to 64, two titres above the controls. This difference turned out to be statistically significant. Exposure to C. pneumoniae with antibodies (IgG) should be considered in any HIV diagnosed patient as a risk factor for atherosclerosis, having found that the inverse geometric averages of antibodies titre are significantly different comparing cases and controls, especially in patients with dyslipidemia, hypertriglyceridemia or in patients whose treatments could cause these conditions. In patients with concomitant hypertriglyceridemia, the association increases up to three times. It is advisable that AIDS patients take a serological test to determine exposure to C. pneumoniae, and to assess treatment options.