The aim of the investigation was to examine differences in the motivational, psychophysiological, psychological and cognitive responses to nonsuicidal selfinjury (NSSI) and other impulsive behaviours of individuals with and without Borderline Personality Disorder (BPD). Also, it was anticipated that results of this investigation could identify whether or not individuals with BPD engage in other impulsive, self-destructive behaviours for the same reasons that they engage in NSSI. Essentially, this part of the research was comprised of an examination of criterion 4 and 5 of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR; APA, 2000) diagnostic criteria for BPD. To examine processes at the time of NSSI and impulsive behaviours, a personalised, staged guided imagery methodology was used to test the affect regulation theory of NSSI. It was expected that both individuals with and without BPD would demonstrate a reduction in negative emotional states with the act of NSSI. However, it was expected that individuals with BPD would report an increase in high arousal positive emotional states, such as excitement, with the act of NSSI whereas individuals without BPD would report an increase in low arousal positive emotional states. This affect regulation function, either positive or negative, also was predicted to distinguish NSSI from control events of an accidental injury and an emotionally neutral event. Interestingly, results indicated that when considering subjective (selfreport) data alone, individuals with BPD and individuals without BPD (NBPD) appeared almost indistinguishable in their responses to NSSI. However, when examining objective (psychophysiological) responses, the two groups demonstrated completely different reactions to NSSI. Individuals without BPD demonstrated a pattern of tension reduction which was consistent with their self-reported reduction in anxiety and tension during the act of NSSI. The BPD group, in contrast, demonstrated the opposite effect, whereby there was an increase in arousal, perhaps suggesting excitement in response to NSSI. Despite this, the BPD group still reported that they felt calm and relaxed as a result of self-injury. This has important considerations for the affective instability of individuals with BPD, particularly in relation to alexithymia. Secondly, a comparison was made between NSSI and other diagnostically relevant, impulsive behaviours. It was expected that engaging in impulsive behaviours would elicit an excitement response for those with BPD, and a tension reducing function for those individuals without BPD. It also was expected that the response to the impulsive behaviours would mirror the arousal increase, excitement response to NSSI in the BPD group and would mirror the arousal decrease, calm response to NSSI in the NBPD group. Similarly, it was thought that the reasons for engaging in the impulsive behaviours will relate to sensation seeking for the BPD group but a sense of calm for the NBPD group. Results indicated that there were few differences between the groups in terms of motivational factors associated with impulsive behaviours and, furthermore, psychophysiological responses to these impulsive behaviours did not mirror those demonstrated for NSSI. Results were discussed in terms of support for the fact that NSSI is a unique behaviour, and should not necessarily be included in the DSM-IVTR (APA, 2000) with other Impulse Control Disorders. Finally, the motivational and cognitive responses to NSSI for those with and without BPD were considered. In particular, consideration was given to internal and external motivations to determine if the presence of BPD has an impact on the reasons why people choose to self-injure. It is evident that people with BPD have additional difficulties with interpersonal communication that are not experienced as intensely by people without BPD (Lieb, Zanarini, Schmahl, Linehan, & Bohus, 2004). It was thought that these difficulties should influence their motivation for engaging in behaviours that serve to regulate affect because the disturbance in affect may be caused by interpersonal difficulties. Results for Study 3 indicated that both of the groups endorsed internal motivations for NSSI, but the BPD group endorsed a number of additional external motivations for NSSI indicating that NSSI may be used as a maladaptive tool for communicating distress. In addition, results indicated that individuals with BPD have a range of additional difficulties with anger, irrational beliefs and perceived low ability to control their emotions which likely contribute to NSSI. Interestingly, the BPD group also endorsed the cognition I like to hurt myself during NSSI, which further supports the notion that the behaviour may be associated with sensation seeking in this group. It was concluded that the role of affect regulation in NSSI needs to consider the role of both positive and negative emotions, as well as increase and decrease in arousal, rather than assume that the affect regulatory function of NSSI is always a decrease in negative emotions. This is likely to have important implications for the consideration of BPD in future research as well as treatment options.