||Self-inflicted injury (SII) is prevalent and debilitating among adolescents. One of the most salient developmental contexts is the parent-child relationship, given its importance for shaping key social and self-regulatory processes that affect SII risk. A key strategy for promoting healthy family interactions is validation, or communicating an understanding of how another came to act, think, or feel. Parent-child relationships involving higher levels of validating responses are associated with adaptive self-regulation, whereas family environments characterized by invalidation and conflict escalation are associated with youth emotion and physiological dysregulation, and SII risk. The current study examines how teaching a validation-oriented skill from Dialectical Behavior Therapy affects behavioral and biological indices of SII risk among self-injuring adolescents and their mothers (n = 30 dyads), and typical control mother-daughter dyads (n = 30). Behavioral indicators of family functioning (e.g., cohesion, positive affect, negative affect, coercion, invalidation, withdrawal) and physiological indices of emotion regulation (respiratory sinus arrhythmia [RSA] responding and reactivity) were examined across conflict and validation-oriented discussion tasks. Results indicated that dyads' subjective affect and behavioral indicators of family functioning generally improved following a manipulation teaching validation particularly among clinical dyads. Participant RSA responding did not significantly differ across study tasks. However, findings indicate mother-, daughter-, and dyad-level behavior accounted for significant variance in RSA reactivity. Understanding the effects of intervention techniques across physiological and behavioral levels of analysis may help guide future prevention efforts and inform treatment for adolescents at high risk for SII.