This study aimed to examine which specific emotion processes influence self-inflicted injury: basal respiratory sinus arrhythmia, baseline negative emotional intensity, emotional reactivity, or emotion regulation deficits. Self-injuring individuals with borderline personality disorder (N = 22) reported their lifetime self-injury frequency. Basal respiratory sinus arrhythmia and baseline skin conductance responses measurements were collected. Participants then either reacted as they usually would (i.e., emotional reactivity), or utilized mindfulness- or distraction-based strategies (i.e., emotion regulation), in response to negative images while self-reported negative emotion and skin conductance were monitored. Higher basal respiratory sinus arrhythmia and baseline emotional intensity predicted higher lifetime self-injury frequency. Chronic, resting emotion processes may be more important targets for reducing self-injury compared to labile, acute emotion processes.