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We studied the course of aggressive behavior in an epidemiologically defined sample of first graders with and without comorbid anxious symptoms. Our primary purpose in doing so was to understand whether the stability of aggression in young children was attenuated or strengthened in the presence of comorbid anxiety. Previous studies of older children and adolescents had produced equivocal findings in this regard. Data on anxious symptoms were obtained through an interview of the children, whereas aggressive behavior was assessed through the use of a teacher interview and peer nominations. Assessments were performed in the fall and spring of first grade. In contrast to children classified as aggressive alone in the fall of first grade, boys and girls classified as aggressive and anxious in the fall of first grade were significantly more likely to be classified as aggressive in the spring in terms of teacher ratings and/or peer nominations of aggression. Thus our findings suggest that the link between early and later aggression may be strengthened in the presence of comorbid anxious symptoms, rather than attenuated. Future studies are needed to identify the mechanisms by which the course of aggression is influenced by the presence of comorbid anxiety.