This study examined both continuity and familial, intrapsychic, and environmental predictors of change in adolescent attachment security across a 2-year period from middle to late adolescence. Assessments included the Adult Attachment Interview, observed mother–adolescent interactions, test-based data, and adolescent self-reports obtained from an ethnically and socioeconomically diverse sample of moderately at-risk adolescents interviewed at ages 16 and 18. Substantial stability in security was identified. Beyond this stability, however, relative declines in attachment security were predicted by adolescents' enmeshed, overpersonalizing behavior with their mothers; depressive symptoms; and poverty status. Results suggest that although security may trend upward for nonstressed adolescents, stressors that overwhelm the capacity for affect regulation and that are not easily assuaged by parents predict relative declines in security over time.