The middle school years are a period of increased risk for youths' engagement in antisocial behaviors, substance use, and affiliation with deviant peers (Dishion & Patterson, 2006). This study examined the specific role of parental monitoring and of family relationships (mother, father, and sibling) that are all critical to the deterrence of problem behavior in early adolescence. The study sample comprised 179 ethnically diverse 6th-grade (46% female) students who were followed through 8th grade. Results indicated that parental monitoring and father-youth connectedness were associated with reductions in problem behavior over time, and conflict with siblings was linked with increases in problem behaviors. No associations were found for mother-youth connectedness. These findings did not differ for boys and for girls, or for families with resident or nonresident fathers. (Contains 2 tables and 2 figures.)