This study explores the developmental trajectory of externalizing problems in a sample of 101children of adolescent mothers from preschool through third grade using hierarchical linearmodels (HLM). First, a detailed assessment of the structure of the developmental trajectory ofexternalizing problems is provided. Second, the impact of three risk factors (infant attachment,maternal depressive symptomatology, and child sex) on the developmental course of externalizingproblems is assessed. Both avoidant and disorganized attachment and higher levels of maternaldepressive symptomatology were associated with higher levels of externalizing problems at 9years of age. Girls also showed higher externalizing problems relative to their same-sex peers thandid boys. In addition, maternal depressive symptomatology related to the rate of change in theseproblems over time; the greater the mother's depression, the faster externalizing problemstended to increase. Although the overall level of maternal depressive symptomatology was relatedto children's externalizing problems for secure, avoidant, and disorganized groups, changesin maternal depressive symptomatology over time predicted levels of externalizing problems onlyfor children with avoidant insecure attachments.