Neuroimaging plays an increasingly important role in the evaluation of dementias of older adults. Although no unequivocal diagnostic test other than biopsy is currently available for Alzheimer's disease and some other dementias during life, neuroimaging techniques are an integral part of the examination and follow-up of patients with dementia. This review describes findings in the brains of patients with normal aging and in elderly patients with dementia, as shown by MR imaging and MR spectroscopy, positron emission tomography (PET), and single-photon emission computed tomography (SPECT) and correlated with clinical and pathologic features.