The diagnostic approach of dementia has clearly improved with the progress in medical imaging, notably magnetic resonance imaging. The conventional T1 and T2 sequences or morphological imaging have demonstrated their interest in the positive and differential diagnosis of dementia, together with the more precise description of normal ageing of the brain. The ANAES (French medicines agency) proposes systematic brain imaging, notably by magnetic resonance imaging (MRI) in their practical guidelines for the diagnosis of Alzheimer's disease (http://www.anaes.fr). THE INTEREST OF CERTAIN IMAGING TECHNIQUES: The therapeutic progress in treatment of dementia implies that the different affections be recognised as early as possible. With this in mind, the functional MRI is capable of describing the damage in cases when morphological imaging is not sufficiently specific. Recent studies have reported the interest of diffusion and perfusion imaging, activation MRI and proton spectroscopy. FROM A THERAPEUTIC POINT OF VIEW: The combination of morphological and functional approaches will provide a better definition of the groups at risk in order to target current treatments and those to come.