The understanding and treatment of severe self-injurious behavior remain problematic. Numerous treatment studies have been conducted in recent years, but there has been a general lack of systematic behavioral analysis prior to intervention. The present study presents a long-term, multifaceted behavior analysis of severe self-injurious behavior in a 13-year old institutionalized retarded boy, together with the results of an effective treatment and cross-setting generalization program. Adult attention was not a significant controlling variable. However, avoidance of task/demands was found to be a critical determinant of self-injurious behavior, aggression, and screaming. These data lend support to the avoidance hypothesis concerning self-injurious behavior and point to the need for its continued investigation. Treatment intervention employed physical punishment (a thigh slap) in a multiple-stimulus, multiple-baseline design. Suppression of self-injurious behavior, aggression, and disruptive behavior was rapid and virtually complete. Generalization to the residential setting was actively programmed, resulting in continued suppression without further need of physical punishment. Ethical, legal, and procedural problems associated with the treatment of self-injurious behavior are also presented and discussed.