Ischemic and hemorrhagic stroke are probably multifactorial diseases. A combination of environmental and genetic risk factors are likely to play a role. The genetic contribution is complex (polygenic; multiple genes), as the presence of common risk factors for stroke, such as diabetes and hypertension, is partly determined by genetic predisposition. All types of stroke (e.g., cortical, subcortical, lacunar and hemorrhagic) can lead to vascular dementia. Consequently, vascular dementia can also be considered to be a complex genetic disease. However, genetic studies on vascular dementia are scarce. Recent studies have focused on monogenic forms of stroke, such as cerebral autosomal dominant arteriopathy with subcortical infarcts, leukoencephalopathy and the amyloid angiopathies. These disorders can probably serve as models to study factors that may also contribute to the common forms of stroke and vascular dementia.