The purpose of this study was to determine whether comorbid adolescent criminal and substance involvement (ACSI) was more predictive of adult criminal/substance involvement than adolescent criminal or substance involvement alone, and identify potential precursors and mediators of this relationship. Using data from 6502 members of the four-wave National Longitudinal Study of Adolescent Health (Add Health), it was found that ACSI at Wave 2 (ages 13-20) predicted adult criminal and substance involvement at Waves 3 (ages 18-26) and 4 (ages 24-32). In addition, antisocial cognition at Wave 3 partially mediated the relationship between ACSI at Wave 2 and criminal/substance involvement at Wave 4 and Wave 1 school problems correlated with the independent, dependent, and mediating variables. Theoretical and practical implications of this study include the role of early school problems in the development of ACSI and the significance of antisocial thinking in maintaining this involvement.