The aim of this article is to describe the nosographical contribution of the Italian psychiatrist Sante De Sanctis (1862-1935) to early twentieth-century child psychiatry. De Sanctis first proposed the category of 'dementia praecocissima' in 1906, and it was recognized by Kraepelin. Dementia praecocissima has its roots in a theoretical and methodological conception of mental disorder based on 'psycho-physical proportionalism' and the 'law of circle'. This article deals with De Sanctis's model, which has so far been neglected by historiographers; it shows the pioneering role that this Italian psychiatrist played in child psychiatry in Italy.
Keywords: 20th century; Child psychiatry; Italy; Sante De Sanctis; dementia praecocissima; neurodevelopmental disorders.