Severe problem behaviors such as aggression, self-injury, and property destruction can result in injury, and require specialized and expensive treatment. This article reviews outcome research published since 1995 that used behavioral techniques to decrease severe problem behaviors among children and adolescents with autism spectrum disorder and/or intellectual disability. Many relatively simple interventions were reported to significantly reduce severe problem behavior, which offers hope for practitioners. Nonetheless, these studies also reveal a risk for injury and a need for specialized assessment and placement, careful tracking, and high-quality treatment that few agencies could likely replicate without increases in training and support.