Our purpose was to investigate the expression of matrix metalloproteinase (MMP)-2 and -9 in all types of abdominal aortic aneurysms (AAA): symptomatic, asymptomatic, and ruptured. MMP-2 and -9 activity was investigated in surgical samples from the arterior wall of 46 AAA, using a standard immunohistochemical technique. The MMP-9 activity was significantly higher in large AAA (>6 cm), but there was no relation between AAA size and MMP-2 activity. Neither MMP-2 nor MMP-9 were related with AAA rupture, other complications or symptoms. The MMP-9 activity in AAA is a determinant of the aneurysm size, but it is not related to clinical manifestations.