Although there has been an increase in research on non-suicidal self-injury (NSSI) there continues to be a need to explore this phenomenon in light of evidence that this behavior is increasing rapidly among adolescent populations. Multiple formulations exist that have gained research support for the onset and maintenance of NSSI; impulsivity, addictive behavior, alexithymia and dissociative symptoms, maladaptive social/interpersonal relationships, personality pathology, and affect regulation. This study examined the affect regulation model proposed by Suyemoto (1998) in a sample (N = 175) of inpatient adolescents using an objective, self-report assessment instrument (PAI-A). This study also examined potential differences between European-American and Latino/a-American participants to test whether the affect regulation model is a useful cross-cultural explanation for NSSI within this sample. Mutivariate analysis revealed no group differences related to ethnicity but participants within the self-injuring group scored significantly lower on the PAI-A subscales that measure aggression with self-injurers scoring lower than their non-injuring counterparts on aggressive attitude, and physical aggression. Results suggest that adolescent inpatient self-injurers may attempt to regulate anger/hostility/aggression by employing self-harm as a maladaptive coping strategy. Results were consistent with previous research studies investigating functions of intentional self-harm.