Earlier studies have indicated an association between blood group non-O and atherosclerosis related vascular diseases. Abdominal aortic aneurysm (AAA) is traditionally regarded as a consequence of atherosclerosis. The aim of the present study was to investigate the association between ABO blood groups and AAA with special regard to a relation to AAA rupture. Prospectively, 504 patients operated on for AAA were investigated. Patients operated on for AAA have similar ABO blood group distributions as a population based control group. Furthermore, there was no significant difference in distribution of ABO blood group between patients operated on for ruptured AAA (n=174) and non-ruptured AAA (n=330). In conclusion, this study fails to demonstrate an association between ABO blood groups and AAA.