Primary degenerative dementia syndromes are an increasingly relevant problem worldwide because of the progressive aging of the population. Their diagnosis is often a challenge for clinicians and, even in the best cases, only a possible or probable diagnosis can be reached. Molecular neuroimaging techniques can be very useful in dementia patients, especially for obtaining a diagnosis in the early stage of disease. The most diffuse and widely available nuclear medicine method for neurological studies is 18F-fluoro-deoxy-glucose (18F-FDG)-PET, which allows the quantification of glucose gray matter metabolism and helps visualize typical, adequately specific, patterns for many kinds of degenerative dementia, not only for the well-known and well-studied Alzheimer’s disease. This paper aims to describe the clinical and 18F-FDG-PET profiles of the principal non-Alzheimer type of degenerative dementias.