This study investigated the role of mutual dislike dyads (MDDs) in the development of aggressive behavior across the middle childhood years. Of particular interest was whether involvement in MDDs predicted later aggression, and whether the magnitude of the association between MDDs and later aggression varied based on characteristics of target children and "others" involved in their MDDs. Data were collected on a community sample of 453 children participating in an ongoing longitudinal study. Classroom peer nomination and rating-scale measures were collected in kindergarten through third grade; aggressive behavior problems were assessed via teacher ratings in the early elementary years (kindergarten and first grade) and late elementary years (fourth and fifth grade). MDD involvement in the middle elementary years (second and third grade) was associated with higher levels of aggression in the late elementary years among boys (but not girls), and these predictions held after controlling for group-level peer disliking in the middle elementary years, aggression in the early elementary years, and demographic variables. The association between MDD involvement and subsequent aggression was also qualified by the aggressiveness of others in children's MDDs: Having more MDDs predicted later aggression only among boys whose MDDs involved mostly non-aggressive others.