Non-suicidal self-injury (NSSI) is highly prevalent and associated with tissue damage, emotional distress, and psychiatric disorders. While often discussed in the context of Borderline Personality Disorder and suicide, research demonstrates that NSSI is distinct from these constructs and should be viewed as an independent diagnostic category. Recently, Non-Suicidal Self-Injury Disorder (NSSID) was included in the revised Diagnostic and Statistical Manual of Mental Disorders as a condition for further study. In this article, we describe the properties of a self-report measure designed to assess proposed criteria for NSSID. Undergraduate students at 2 large, public universities completed the NSSID Scale (NSSIDS) along with other measures of NSSI characteristics and psychopathology. Among participants with a history of NSSI, approximately half (54.55%) met diagnostic criteria for NSSID. Participants were most frequently excluded from an NSSID diagnosis on the basis of criterion A (frequency of NSSI) and criterion E (distress or impairment related to NSSI), while participants were least likely to be excluded from diagnosis on the basis of criterion D (NSSI method exclusions) and criterion F (diagnostic rule-outs). Consistent with previous literature, the most commonly reported precipitants to NSSI were negative feelings or thoughts (criterion C2). Participants who met criteria for NSSID reported more severe depression, anxiety, and NSSI than participants who engaged in NSSI but did not meet criteria for NSSID. These results support the use of the NSSIDS as a reliable and valid self-report measure of NSSID symptoms.