Self-mutilators' psychophysiological and subjective responses during an imaged self-mutilative act were examined. Differences in arousal to 3 imaged control events (neutral, accidental injury, and aggression) were examined between 3 self-mutilation groups (prisoner, prisoner control, and non-prison control). Imagery scripts were presented in 4 stages: scene setting, approach, incident, and consequence. Results indicated a decrease in psychophysiological and subjective response during self-mutilation imagery. No such decrease was evident for nonmutilators who we administered standard self-mutilation imagery. A lag between psychophysiological and psychological response to the self-mutilative act was evident. Responses elicited during self-mutilation imagery were different from those of control imagery. Results indicated that self-mutilative behavior is maintained by its reinforcing tension-reducing qualities.