Williams syndrome (WS) is a genetic disorder causing intellectual disability. Children with WS often exhibit various kinds of maladaptive behaviours that affect their social functioning. In order to determine whether these behaviours are syndrome-specific, it would be necessary to compare children with WS with children with other syndromes as well as to provide data on the socio-emotional profile in WS from a variety of cultures. The present study investigated the behavioural profile and its relation to maternal stress in Greek young children with WS in comparison with young children with Down syndrome and typically developing (TD) children.