Dementia is a syndrome–usually of a chronic or progressive nature–in which there is deterioration in cognitive function beyond what might be expected from normal ageing (WHO). As the world population ages, the number of people afflicted with dementing illnesses will increase. This neurodegenerative disease is one of the major causes of disability and dependency among older people worldwide. Brain single-photon emission computed tomography (SPECT) allows the study of regional cerebral blood flow, providing functional information. Each of the different types of dementia has a distinct blood flow pattern that is revealed with SPECT imaging and which can be used for differential diagnoses. This imaging technique can also be used to differentiate dementia from pseudodementia. The use of SPECT has been recommended in various guidelines to help in differential diagnosis of dementia. The National Institute for Health and Clinical Excellence in the UK recommend the use of SPECT or positron emission tomography (PET) to help differentiate Alzheimer's disease (AD) from frontotemporal dementia and vascular dementia when there is diagnostic doubt (NICE, 2006). The European Federation of the Neurological Societies guidelines for diagnosis also supports the use of FDG-PET (18F fluorodeoxyglucose positron emission tomography) or perfusion SPECT when clarifying a diagnosis of AD. This review describes the utility of perfusion SPECT in differential diagnosis of neurodegenerative dementias.