Objective. To make a critical evaluation of the relation between a low educational level and dementia in order to determine whether this is a real risk factor for the development of dementia. Development. We review the available epidemiological evidence for and against this, paying particular attention to any possible bias which might account for the association found As a second step we analysed, from the point of view of the cause, the relation between low educational level and dementia so as to obtain a theoretical framework for the mechanisms by which a low educational level acts. Finally, we discuss the social-health relevance of this risk factor. Conclusions. A low educational level, especially illiteracy is the most important social-health risk factor for dementia, not only because of its high prevalence and degree of association, but also because of the capacity of society to manipulate it. Certain educational policies, including those concerning the adult population, may have a marked social-health effect and require study and evaluation.