The aim of this study was to investigate the role of social capital assessed in early adulthood in linking self-control in childhood with psychological and social functioning in middle age. Data collected at ages 8, 27, and 42 years were based on the Jyvaskyla Longitudinal Study of Personality and Social Development (159 females, 177 males). Self-control was assessed at age 8 using teacher ratings and peer nominations. Social capital at age 27 was operationalized in terms of the breadth of the individuals' social network and the depth of their close relationships. Psychological functioning at age 42 was indicated by, for instance, psychological well-being, and social functioning was indicated by, for instance, aggression. Results showed for females, but not for males, that social capital partially mediated the link between self-control and psychological well-being, as well as the link between self-control and aggression. In females, higher self-control explained better psychological well-being and lower aggression both directly and indirectly via the breadth of the individual's social network. In males, both childhood self-control and behavioral activity contributed to the breadth of their social network, which, in turn, contributed to the depth of their close relationships. Deeper relationships explained better psychological well-being and, marginally, lower aggression; male lower aggression was directly accounted for by childhood self-control. (Contains 2 tables, and 4 figures.)