Positron emission tomography (PET) imaging of [18F]-2-fluoro-2-deoxy-D-glucose (FDG) is accurate in the early detection of Alzheimer's disease (AD) and in the differentiation of AD from the other causes of dementia. FDG-PET imaging is available widely and performed easily. Different patterns of abnormality with the various causes of dementia are well described. Semiquantitative methods of image interpretation are available. Medicare covers FDG-PET imaging for the narrow indication of differentiation of possible AD from frontotemporal dementia.