In a review of results of clinical observations, girls from 2:03 (yrs:mos) at stages III and IV of the Rett syndrome (RS) and autistic children from 4:01 with or without severe mental retardation were compared as to their behavioral traits. Signs of concordance between the extremely low mental, affective and motor developmental levels, such as in the expression of the eyes, are a prominent feature of RS, whereas signs of higher cortical functions that are in contrast with insufficient relations to objects, people and space are a prominent characteristic in autism. It is argued that insistence on sameness, avoidance of social stimuli and self-injurious stereotypies of autistic children are neurotic reactions based on their insufficient object relations. On the basis of the clinical findings a theory is proposed, according to which there exists a system for involuntary contributions to the affective engagement in perception, which is insufficiently developed in autism and in earlier stages of RS. Regarding its structure and function, it is analogous to the phylogenetically old extrapyramidal system and its necessary involuntary emotional contributions to all voluntary movements and postures.