Abstract Alzheimer’s disease (AD) has heterogeneous pathology, in part due to the large subset of cases (AD+CVD) with superimposed vascular lesions that are sufficient in number and distribution to accelerate the clinical course of dementia. Brains with AD+CVD have lower densities of neurofibrillary tangles and Aβ-amyloid diffuse plaques, and increased numbers of cerebral vessels exhibiting p53-associated apoptosis relative to brains with uncomplicated AD. AD and AD+CVD both exhibit altered expression of the nitric oxide synthase 3 (NOS-III) gene; however, in AD+CVD, reduced NOS-III expression in cerebral vessels is associated with an increased frequency of vascular lesions, vascular smooth muscle cell apoptosis, and Aβ-amyloid plaques. In contrast, experimental and spontaneous focal acute and subacute cerebral infarcts are associated with increased NOS-III expression in perifocal neurons, glial cells, cerebrovascular smooth muscle and endothelial cells, and diffuse Aβ-amyloid plaque formation. This suggests that ischemic injury and oxidative stress can precipitate NOS-III-mediated cell loss and neurodegeneration. A role for aging-associated impaired mitochondrial function as a contributing factor in AD and CVD is suggested by the reduced levels of mitochondrial protein observed in AD and AD+CVD cortical neurons and vascular smooth muscle and endothelial cells. The aggregate findings suggest that cell loss and neurodegeneration may be mediated by somewhat distinct but overlapping mechanisms in AD and AD+CVD.