INTRODUCTION: A growing number of studies have found evidence that anxiety and depressive disorders are associated with atypical amygdala hyperactivation, which decreases with effective treatment. Interest has emerged in this phenomenon as a possible biological marker for individuals who are likely to benefit from tailored treatment approaches. OBJECTIVE: The present study was designed to examine relationships between pretreatment amygdala activity and treatment response in a sample of anxious children and adolescents. MATERIALS AND METHODS: Participants, who were diagnosed predominantly with generalized anxiety disorder (GAD), underwent functional magnetic resonance imaging (fMRI) scanning before treatment with fluoxetine or cognitive behavioral therapy (CBT). RESULTS: Results indicated significant negative associations between degree of left amygdala activation and measures of posttreatment symptom improvement in the group, as a whole. DISCUSSION: Taken together with research on associations between adult amygdala activation and treatment response, these findings suggest that patients whose pretreatment amygdala activity is the strongest may be particularly likely to respond well to such widely used treatments as selective serotonin reuptake inhibitor (SSRI) medications and CBT.