Recent progress in diagnostic imaging techniques has greatly contributed to the elucidation of pathophysiology, as well as differential diagnosis in dementia. In particular, X-ray computed tomography (CT) offers the ability to detect morphological changes of the brain, whereby making it possible to differentiate between cerebrovascular and degenerative dementias. Magnetic resonance imaging (MRI) allows three-dimensional visualization of gyrus atrophy, providing the ability to depict subcortical minor infarcts and white matter lesions. The advent of positron emission tomography (PET) and single photon emission computed tomography (SPECT) has led to a dramatic progression in the search for pathophysiology of dementia. The purpose of this paper is to outline the recent findings of diagnostic imaging modalities, such as X-ray CT, MRI, PET and SPECT, focusing on those in commonly observed cerebrovascular dementia and in degenerative dementias that are projected to increase. Degenerative dementias cover Alzheimer's disease, Pick's disease, Huntington's disease, progressive supranuclear palsy, Parkinson's disease, and normal pressure hydrocephalus. (N.K.) 90 refs.