The results indicate the parallel processes growth model fits the data well. Youths who reported higher delinquent involvement also reported higher drug use over time. Delinquency appears to have significant contemporaneous effects on drug use, such that drug use is exacerbated by delinquent behavior. These findings support existing literature that finds a positive correlation between substance use and delinquency. It makes a unique contribution to the literature by examining the trajectories of drug use in conjunction with those of delinquency among justice-involved youths. The results underscore the importance of interventions that target multiple changing problems these at-risk youth may be experiencing. The prevalence of substance use is particularly disturbing among delinquent youth. Research has consistently identified a strong positive association between drug use and delinquency. This study examined a growth model that simultaneously examined the relationship between growth factors for self-reported heavy alcohol and marijuana use and growth factors for self-reported delinquency among justice-involved youth during a 4-year period. Tables, figure, references