Self-injurious behavior is commonly observed among persons with intellectual disabilities. However, a second parallel use of this term is used in the general mental health field for self-mutilation. The authors describe these two disorders and how they differ. Characteristics of what we refer to as repetitive self-injurious behavior among persons with intellectual disabilities and risk factors for these behaviors are discussed. We also describe different assessment/testing methods which aid in defining this phenomenon. The implications of these data for research and clinical practice are discussed.