An epidemiological study is outlined that shows that Kanner's syndrome is one group among a wider range of children, all with impairment of social interaction, communication, and imagination. Most, but not all, children with this triad of impairments are severely mentally retarded, although severe retardation also occurs in those who are sociable and communicative. It is hypothesized that the socially impaired lack certain abilities that are inborn in normal children and the sociable mentally retarded: namely, the capacity to produce and monitor the normal species-specific preverbal sounds, the drive to explore the environment and form concepts to explain experiences, and the ability to recognize that other human beings are of special interest and importance. A possible neurological basis for these problems is briefly considered.