This article presents current evidence describing the epidemiology, course, functions, and psychiatric co-morbidities of non-suicidal self-injury (NSSI) in adolescents. Rates of NSSI in adolescents have risen recently; studies suggest this rise can be partially attributed to subclinical and experimental forms of NSSI. In light of this trend, assessment of adolescent NSSI behaviors by nurse practitioners is an important step in providing mental health services to adolescents who need them. In this article, Macdonald’s “Stages of Adolescent Substance Use” is adapted to a model of adolescent self-injury called “Stages of Adolescent NSSI Behavior,” and clinical responses according to each stage are proposed.