Parasuicidal behavior in adolescence marks significant risk for later suicide and may represent a precursor to the development of borderline personality disorder (BPD). Current theories of parasuicide and BPD suggest that emotion dysregulation underlies the act of self-harm, which serves to regulate overwhelming negative affect. However, no studies have thoroughly explored an emotion dysregulation model of parasuicide, including both cognitive and physiological measures of this trait. The proposed research will compare parasuicidal teens with normal controls and a clinical comparison group with major depressive disorder (n=25/group) on behavioral and physiological measures of emotion regulation. Adolescents and their parent will complete interviews and self-report measures of emotion regulation, psychopathology, substance use and abuse, and histories of parasuicidal behavior. Physiological assessments will be conducted with both the parent and adolescent during baseline, an emotionally evocative film clip from "The Champ," and a problem-solving discussion. Physiological indices include electrodermal responding (EDR), respiratory sinus arrhythmia (RSA), and cardiac pre-ejection period (PEP).