Biographical data can register differential information about individuals and can invoke a post hoc view of their development. The Autobiographical Data Form was utilized to examine the development and behavioral antecedents associated with neuroticism and extraversion. Subjects were 1030 males and 901 females, all first year college students. Neuroticism was assessed by the total score on the Neuroticism scale of the Maudsley Personality Inventory. Extraversion was similarly assessed by the total score on the Extraversion scale of the same inventory. It was hypothesized that clusters, comprised of items from the Autobiographical Data Form which correlated significantly with each of the criteria, would identify the antecedents. The resulting clusters associated with neuroticism conveyed information about perceived parental expectations and evaluations, mode of disciplinary control, parental affective reactions and family relations. Prior behaviors antedating neuroticism included emotional functions, adjustment modes, psychological needs and social maturity. Physical health, academic performance and attitudes, work and leisure time interests were also identified. With regard to extraversion, 45 clusters resulted, dealing with parental training, standards and socialization practices, intimate behaviors, socioeconomic indicators and relations with important others. Behavioral antecedents of extraversion, were found to be reliance on people, extensive participation in diverse activities and leadership tendencies, self-reliance, inquisitiveness and interests in many subjects. Feelings of self-satisfaction and good health, were likely to be present in the lives of many extraverts. © 1991.