In this study, the validity of a self-report measure of children's perceived attachment security (the Kerns Security Scale) was tested using adolescents. With regards to predictive validity, the Security Scale was significantly associated with (1) observed mother-adolescent interactions during conflict and (2) parent- and teacher-rated social competence. With regards to convergent validity, the Security Scale was significantly associated with all subscales of the Adult Attachment Scale (i.e., Depend, Anxiety, and Close) as measured 3 years later. Further, these links were found even after controlling for mother-child relationship quality as assessed by the Inventory of Parent and Peer Attachment (IPPA), and chi-square difference tests indicated that the Security Scale was generally a stronger predictor as compared to the IPPA. These results suggest that the Security Scale can be used to assess perceived attachment security across both childhood and adolescence, and thus could contribute significantly to developmental research during this period. (Contains 2 tables.)