Frequencies of blood groups (ABO, Rh, MNSs, P, Kell, Lewis and Duffy) and HLA antigens were studied in a series of patients from northern Sweden with abdominal aortic aneurysms. The following significant differences from the controls were found: a decreased frequency of the Rh-negative blood group and increased frequencies of the Kell-positive and MN blood groups. Previously reported associations with the ABO and Rh systems were not confirmed.