Schizophrenia is associated with severe deficits in social functioning. Similar deficits may be present prior to psychosis onset, in childhood and adolescence. If so, then prepsychosis social deficits could provide clues to the development of pathological processes in preschizophrenia children and could potentially improve early identification of the disorder and suggest targets for intervention. Evidence is reviewed from birth cohort, case- control, and familial high-risk studies within distinct periods of development to clarify the nature, timing, and specificity of social deficits in preschizophrenia children and adolescents. The results indicate that poor social functioning does differentiate preschizophrenia children and adolescents from their peers and can be a sensitive and potentially specific predictor of schizophrenia, not just psychopathology in general. Furthermore, age (but not sex) appears to be an important moderator of the strength and specificity of the association between particular social deficits (e.g., externalizing, internalizing) and later schizophrenia. Results are discussed in the context of current developmental theories of timing and pathophysiology of schizophrenia involving hypothalamic- pituitary-adrenal dysregulation. Implications for the early identification and treatment of preschizophrenia individuals are also considered. (Contains 12 footnotes and 4 tables.)