Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) is involved in vascular endothelial damage as well as in the vascular degeneration underlying diabetes mellitus and Alzheimer's disease (AD). Recent evidence suggests that classic pathological features of AD are more pronounced in diabetic mellitus patients. To investigate the expression and distribution of SSAO/VAP-1 in the two pathologies, we have performed an immunohistochemical study in human hippocampal vessels of AD, AD with diabetic mellitus (ADD), diabetic mellitus (DM), and nondemented (ND) patients. The present results demonstrate major vessel accumulation of both SSAO/VAP-1 and amyloid-β immunolabeling intensity in ADD compared with AD patients. Interestingly, nearly damaged vessels with high levels of SSAO/VAP-1 also showed increased oxidative damage markers (AGE, RAGE, and SOD-1) and glial activation (GFAP and HLA). Overall, this work suggests that high vascular SSAO/VAP-1 levels in human hippocampus may contribute to vascular degeneration, which can explain the severe progression in patients with both pathologies. © 2012 Wiley Periodicals, Inc.