Background: Working for pay is associated with substance use and delinquency among older adolescents, although information is scant about younger youth who work. This study investigates associations between self-reports of having a job and substance use and delinquent behaviors in a sample of U.S. 5th graders. Methods: A total of 5147 5th graders and their parents from three large metropolitan areas were assessed in a cross-sectional survey between Fall 2004 and Summer 2006. Multivariate regression was used to estimate associations between having a job and substance use and delinquency. Analyses were conducted in Fall 2007. Results: Twenty-one percent of 5th graders reported having a job, with most working <5 hours per week. Typical jobs included yard work, babysitting, and cleaning. In multivariate models that controlled for demographic characteristics, household composition, and household income, having a job was significantly associated with past-30-day use of tobacco (OR=2.2), alcohol (OR=1.7), and marijuana (OR=3.1). Having a job was also significantly associated with ever being in a fight (OR=1.5) and with running away from home (OR=1.8). Further analyses indicated that the associations between holding a job and delinquency outcomes were driven largely by young workers who worked >2 hours per week. Conclusions: Among 5th graders, having a job was associated with substance-using behaviors and delinquency. Clinicians should consider asking young patients whether they work, and stress to parents the importance of monitoring the work activities, workplaces, and associates of their children. © 2009 American Journal of Preventive Medicine.