<p>Although the pathogenesis of abdominal aortic aneurysm (AAA) remains largely unclear, evidence is accumulating to suggest the systemic nature of this disease. Here, we comprehensively assessed the whole aortic tree with its major branches based on computed tomography angiography (CTA) in AAA patients compared to ascending thoracic aortic aneurysm (ATAA) patients and nonaneurysmal controls, as well as in an original mouse model of AAA in <i>Lkb1</i>^{<i>flox/flox</i>};<i>Myh11-Cre/ERT2</i> mice. The morphology and dimensions of the whole aorta (at different levels) and its major branches were compared among 47 AAA patients, 47 ATAA patients, and 46 nonaneurysmal controls based on CTA images. To further characterize AAA growth, tamoxifen-inducible <i>Lkb1</i>^{<i>flox/flox</i>};<i>Myh11-Cre/ERT2</i> mice were generated. CTA, magnetic resonance imaging (MRI), and histopathological examination were performed to evaluate the morphology and dimensions of the whole aortic tree in <i>Lkb1</i>^{<i>flox/flox</i>};<i>Myh11-Cre/ERT2</i> mice. The whole aorta extending from the sinotubular junction of the aortic root to the terminal aortic bifurcation, along with its major branches, was diffusely enlarged in AAA patients, whereas the dilatation was localized and restricted to the ascending aorta in ATAA patients. <i>Lkb1</i>^{<i>flox/flox</i>};<i>Myh11-Cre/ERT2</i> mice spontaneously and progressively developed AAA, accompanied by aneurysms in renal artery, iliac artery, caudal artery, or femoral artery. Moreover, the mean cross-sectional diameters of the whole aortic tree with its major branches were diffusely larger in <i>Lkb1</i>^{<i>flox/flox</i>};<i>Myh11-Cre/ERT2</i> mice compared with wild-type mice. This original morphologic study demonstrated that abdominal but not thoracic aortic aneurysm is a systemic and generalized arteriomegaly both in mice and humans.</p>