During the 4 years of adolescence, there was a statistically significant decrease in the estimated mean levels of interpersonal callousness (IC), characterized as being deceitful, manipulative, grandiose, superficially charming, lacking empathy and guilt, and not accepting responsibility for transgressions; however, there was substantial individual variation in IC growth trajectories, with some individuals experiencing rapid declines in IC and others experiencing increases in IC during adolescence. Trajectories of IC during adolescence were unrelated to adult emotional problems; however, boys with higher levels of IC in early adolescence (about age 14), as well as those who had less substantial declines or increases in IC during adolescence (ages 14 to 18), had the highest levels of antisocial-personality characteristics in early adulthood (about age 26). A dysfunctional parent-child communication style emerged as the most robust predictor of chronic levels of IC across time. On the other hand, there was no evidence that exposure to delinquent peers or prosocial peers significantly influenced changes in boys' IC during adolescence. The study used data collected from the Pittsburgh Youth Study, a longitudinal study designed to explore the development of delinquency, substance use, and mental health problems in boys. All measures of demographic characteristics, early childhood behavioral problems, parenting practices, and peer variables were collected during the first followup assessment of the oldest cohort, which occurred 6 months after the screening assessment. Information on the early adult outcomes of emotional problems and antisocial personality were collected when the cohort was in the mid-20s. 3 figures, 2 tables, and 70 references