A meta-analytic review was conducted to explain divergent findings on the relation between children's aggressive behavior and hostile attribution of intent to peers. Forty-one studies with 6,017 participants were included in the analysis. Ten studies concerned representative samples from the general population, 24 studies compared nonaggressive to extremely aggressive nonreferred samples, and 7 studies compared nonreferred samples with children referred for aggressive behavior problems. A robust significant association between hostile attribution of intent and aggressive behavior was found. Effect sizes differed considerably between studies. Larger effects were associated with more severe aggressive behavior, rejection by peers as one of the selection criteria, inclusion of 8- to-12-year-old participants, and absence of control for intelligence. Video and picture presentation of stimuli were associated with smaller effect sizes than was audio presentation. Staging of actual social interactions was associated with the largest effects. The importance of understanding moderators of effect size for theory development is stressed.