Concurrent and predictive relationships between peer harassment and problem behavior were examined for middle and high school students as well as gender differences in these relationships. Students recruited in fifth through seventh grades (n = 223) and their parents provided quarterly questionnaire data and were followed up into high school. As hypothesized, experiencing frequent peer harassment in middle school was associated with greater problem behavior concurrently and prospectively into high school. Students experiencing frequent harassment exhibited more aggressive and antisocial behavior and were more likely to associate with deviant peers and use cigarettes during middle school than those experiencing some or no harassment. In regression analyses, frequent verbal harassment predicted antisocial behavior, alcohol use, and deviant peer association in high school, and frequent physical harassment predicted later antisocial behavior, aggression, deviant peer association, and multiple problem behavior. Gender interactions were found for prediction of later aggressive and antisocial behavior.