Dementia is a global health problem with a huge impact on the lives of those afflicted. There are several distinct diseases that are classified under the umbrella term "dementia" ranging from neurodegenerative disorders such as Alzheimer's disease to chronic infections of the central nervous system such as subacute sclerosing panencephalitis ( SSPE), a rare complication of measles virus infection in childhood. Clinical features, neuropsychological profiles and imaging characteristics of the various dementia syndromes can be sufficiently distinct to distinguish them from one another. However, in some cases, the cognitive, psychiatric and behavioural features can sufficiently overlap such that neurophysiologic testing may be of help. While it is recognized the electroencephalogram ( EEG) may have a special role to play in the diagnosis of certain dementing illnesses such as SSPE and Creutzfeldt-Jakob disease (CJD) that have characteristic EEG changes, current research focusses on the potential utility of quantitative EEG as one more tool in the armamentarium of clinicians dealing with patients who suffer from a dementing illness. We searched PubMed and the Cochrane Database from 1 January 1946 up to 1 January 2016, combining the search terms "EEG," "electroencephalography," "dementia" and "status epilepticus"; identified papers from these searches were then read in detail and summarized. Here, we discuss both the qualitative and quantitative EEG findings in the various types of dementia.