Systematic research into the precise nature and the correlates of the social deficits of the autistic syndrome is only of recent date. A survey is presented of developments in research in diagnostics and epidemiology, genetics, social behavior and social cognitions of autism. Studies of siblings of autistic children as well as twin studies support a hereditary basis of autism that might comprise subtle cognitive or social deficits. Behavior observation studies indicate that autistic children lack joint attention gestures in their social behavior repertoire. Research into social cognitions has found some evidence for two hypotheses, i.e. the theory of mind hypothesis and the emotion-recognition hypothesis.