Increased awareness of the heterogeneity among alcohol and drug abusers has led to examination of the influence of concomitant psychopathology on the course of addiction and addictive relapse. Research among adult alcohol and drug abusers has found a detrimental influence of comorbid psychopathology on treatment outcome. Evidence exists for prevalent comorbidity, in particular conduct disorder (CD), among clinical samples of teen alcohol and drug abusers. However, little information is currently available on the relation and influence of psychopathology on outcome after treatment for adolescent alcohol and drug abuse. The current study examines the relation between CD, as assessed by the extent of preadolescent CD behaviors occurring before the initiation of drug use, and outcome for 131 adolescents over 2 years after inpatient treatment for alcohol and drug abuse. Drawing on recent conceptualizations of the process of relapse and progression of addictive behavior, CD is hypothesized to influence the process of relapse by altering coping efforts and intentions and increasing exposure to potential relapse situations. Results reveal that the extent of preadolescent CD behaviors is positively related to alcohol involvement in the 2 years after treatment, and that much of this relation is accounted for by posttreatment cognitive coping, motivation for alcohol abstinence, interpersonal problems, and exposure to alcohol use. Contrary to expectations, preadolescent CD behaviors did not predict posttreatment drug use. These findings provide evidence for the influence of psychopathology on the process of relapse and progression of addiction after treatment for adolescent alcohol and drug abuse, and suggest that teens with early life CD behaviors may be at greater risk for continued alcohol abuse.