Background The Interpersonal Theory of Suicide states that to make a serious or lethal suicide attempt a person must experience reductions in fear and pain sensitivity sufficient to overcome self preservation reflexes (i.e., the acquired capability for suicide). The purpose of the current study was to examine the fearlessness component of the acquired capability for suicide using self-report assessment instruments and an objective measure of aversion (the affectively modulated startle reflex task). Methods Depressed suicide ideators (n = 15), depressed suicide attempters (n = 15), and a group of control participants (n = 14) were compared on their self-report of acquired capability and painful and provocative life events and completed the affectively modulated startle reflex task. This task compared electromyography recordings of participants’ eye-blink response to a startle probe while viewing pictures of varying hedonic valence (neutral, positive, negative, and suicide-related). Results Suicide attempters reported the highest levels of fearlessness and pain insensitivity and a greater history of painful and provocative life events. While no group differences were found on the psychophysiology data, participants reacted to suicide-related images with less aversion compared to neutral images with no differences between suicide-related and positive images. Conclusions Self-reported fearlessness and pain insensitivity can differentiate suicide attempters and suicide ideators. Results suggest that one’s self-perception (i.e., cognitions regarding fear and pain tolerance) are more functionally related to suicide attempts than psychophysiological reactivity to suicide-related stimuli.