Atrophy and cerebrovascular disease are the two most important magnetic resonance imaging (MRI) characteristics in the evaluation of dementia. On MRI, atrophy is the primary hallmark of neurodegenerative dementias including Alzheimer's disease (AD), while vascular dementia is characterized by the presence of ischemic vascular damage, such as territorial infarcts, lacunes, and white matter hyperintensities. Evidence is accumulating that vascular factors play an important role in the development of cognitive decline at old age and clinical AD. In the present article we present results of four recent MRI studies suggesting the additional involvement of small vessel disease in neurodegenerative disorders. Atrophy in the medial temporal lobe, as typically observed in AD, and small vessel disease often coincide. In terms of clinical significance, their effects may even be synergistic. The strict distinction between AD and vascular dementia is often artificial, as most patients suffer from both disorders to some extent. For the future, we see an important role for MRI in identifying those different compartments, regardless of clinical classification. Treatment could be directed by (and evaluated through) MRI patterns, rather than a diagnostic label.