Dementia is the progressive loss of intellectual functions due to involvement of cortical or subcortical areas. Specific involvement of certain brain areas in the different diseases leads to impairment of different functions, e. g., memory, language, visuospatial abilities, and behavior. Magnetic resonance imaging and other neuroradiological studies may indicate which structures are mainly or selectively involved in a demented patient, thus allowing clinical-radiological correlations. Clinical presentation and evolution of the disease, supported by imaging studies, may lead to a highly probable diagnosis. The most common disorders, or the most relevant from the neuroradiological point of view, such as Alzheimer's disease, frontotemporal dementia, vascular dementias, dementia associated with parkinsonism, Huntington's disease, Creutzfeldt-Jakob disease, and normal-pressure hydrocephalus, are briefly discussed.