Adolescent delinquency, drug use and aggression remain societal concerns. These problems are more common with adolescent boys than girls, and tend to increase with age. Although a lack of parental monitoring has been found to be related to problem behaviors, the mediating role of monitoring on the relationship of sex and grade to problem behaviors has not been directly studied. This paper examined parental monitoring as a mediator of the relationship of sex and age to delinquency, drug use, and aggression in a sample of urban African American young adolescents. Our findings indicated that in general, boys and older adolescents reported higher rates of delinquency, drug use, and aggressiveness. Boys and older adolescents also indicated less monitoring by parents. Parental monitoring was found to mediate the effects of sex and grade on some of the behavioral problems.