Attachment theorists suggest that attachment security with parents supports the quality of social adaptation in peer groups during early childhood, and numerous studies supporting this conjecture have been published. Most of these studies used enacted representations rather than mental representations of attachment security, and most studies examining mental representations used adult (parent or teacher) ratings of peer-group adaptation. Our study tested relations between preschool children's (N = 147; age 48-69 months) mental representations of attachment by using the Attachment Story Completion Task and child-level indicators of social competence based on direct observations and sociometric interviews. General intelligence tests were administered to control for effects of developmental level on child narrative production. Analyses revealed positive, significant associations between attachment measures and all social competence composites. Children with more secure attachment representations were more socially engaged and more likely to exhibit social, emotional, and cognitive skills that contribute to peer acceptance. Results support the hypothesis that attachment security is a foundational support for peer social competence.