Intentional self-harm behavior is an important clinical phenomenon that appears highly related to borderline personality disorder (BPD). Self-harm behavior in the context of borderline personality probably exists along a continuum from graphic, self-harm behavior to milder forms of self-sabotaging behavior that might be viewed as self-defeating. Relatively little attention has been paid to developing a self-report measure of intentional self-harm, particularly as a screening device for detecting BPD. In Study 1, an initial list of self-harm behaviors encountered in clinical practice was narrowed to those behaviors related to BPD in a sample comprised of adults from both a mental health and non–mental health setting. All participants (N = 221) underwent a semistructured diagnostic interview for BPD. Using a cut-off score of 5 on the resulting 22-item Self-Harm Inventory (SHI), 83.7% of research participants were correctly classified as having BPD or not. In Study 2, women (N = 285) sampled from an outpatient medical setting completed the SHI and a widely used self-report measure of BPD. The SHI cut-off score resulted in correct classification of 87.9% of the individuals. In Study 3, using a sample of adults involuntarily hospitalized for psychiatric reasons (N = 32), the SHI performed at least as well as another self-report measure of BPD in diagnosing participants (the final diagnosis was based on a semistructured interview). The results are discussed with regard to potential advantages and utility of the SHI and need for further validation. © 1998 John Wiley & Sons, Inc. J Clin Psychol 54: 973–983, 1998.