In this article, the author provides a practice-friendly guide to the psychological assessment of self-injury, such as self-inflicted cutting, burning, hitting, and excoriation of wounds. The crucial distinction between self-injury and suicide is emphasized. The author presents a structure for the assessment of self-injury that focuses first on the therapeutic relationship, and thereafter on the history and specifics of the behavior, its intrapersonal and interpersonal functions, and its antecedents and consequences. Types of self-injury that are atypical, and especially alarming, are identified. A case example illustrates both the style and content of a thorough assessment.