This study explores reciprocal relations between children's attachment representations and their cognitive ability. Previous literature has mainly focused on the prediction of cognitive abilities from attachment, rarely on the reverse prediction. This was explored in the current research. Attachment representations were assessed with the Attachment Story Completion Task (Bretherton, Ridgeway, & Cassidy, 1990); the IQ was measured with the WPPSI-III (Wechsler, 2004). Data were collected twice, at a two-year interval, from about 400 preschoolers. Reasoning IQ was found to influence the development of secure attachment representations, while attachment security and disorganization influenced later verbal IQ. The implications of the findings for both clinical and research purposes are discussed in the light of the interactions between cognitive abilities and attachment representations. (Contains 3 tables and 1 figure.)