Nonsuicidal self-injury (NSSI) is an issue primarily of concern in adolescents and young adults. Thus far, no single NSSI self-report measure offers a fully comprehensive assessment of NSSI, particularly including measurement of both its functions and potential addictive features. The Ottawa Self-Injury Inventory (OSI) permits simultaneous assessment of both these characteristics; the current study examined the psychometric properties of this measure in a sample of 149 young adults in a university student sample (82.6% girls, Mage = 19.43 years). Exploratory factor analyses revealed 4 functions factors (internal emotion regulation, social influence, external emotion regulation, and sensation seeking) and a single addictive features factor. Convergent evidence for the functions factor scores was demonstrated through significant correlations with an existing measure of NSSI functions and indicators of psychological well-being, risky behaviors, and context and frequency of NSSI behaviors. Convergent evidence was also shown for the addictive features scores, through associations with NSSI frequency, feeling relieved following NSSI, and inability to resist NSSI urges. Additional comment is made regarding the potential for addictive features of NSSI to be both negatively and positively reinforcing. Results show preliminary psychometric support for the OSI as a valid and reliable assessment tool to be used in both research and clinical contexts. The OSI can provide important information for case formulation and treatment planning, given the comprehensive and all-inclusive nature of its assessment capacities.