Single photon emission computed tomography (SPECT) and positron emission tomography (PET) are important tools in the differential diagnosis and therapeutic monitoring of cognitive disorders. SPECT and PET are highly sensitive methods for the early diagnosis of underlying neurodegeneration and the functional changes in the basal ganglia. Early and reliable diagnosis will become even more relevant with the development of options in the causal treatment of dementias, which would exert their most beneficial effects well before the onset of clinical symptoms. This review provides a brief survey on currently available methods of nuclear imaging in cortical (Alzheimer's disease) and subcortical forms of neurodegenerative dementia (Parkinson's disease; dementia with Lewy bodies).