Serious juvenile delinquency consists of actions which cause or pose real, rather than potential, threats of bodily injury to the actor or to others. Such behavior may include homicide, armed robbery, forciple rape, arson, kidnapping, and assault, particularly aggravated assault. Serious juvenile offenders also include chronic repeaters of offenses, such as larceny, which may cause injury to others. Youths arrested for serious crimes in 1978 were usually white males, but over half of the youths arrested for violent offenses were blacks or other minority group members. Data from several sources indicate that serious juvenile delinquents come from deteriorated urban neighborhoods and families of low socioeconomic status. Their families generally have only one parent at home or are tense, hostile, and abusive, and parenting is poor. Serious delinquents have assaultive tendencies and have had few successful experiences at school. Delinquents who commit serious offenses are generally repeat offenders whose encounters with juvenile authorities have not induced them to change their illegal behavior. No treatment programs are currently provided specifically for this group, although some programs for juvenile offenders include serious offenders. Critical factors associated with the provision of quality services for serious juvenile offenders in any secure care program include (1) a population of 15 or less; (2) a low-profile security design rather than a traditional design; (3) flexible organization and use of resources, with programming that reflects quality services and program standards; (4) high quality and competent staff; and (5) humane and efficient administration based on a centralized management information system, specific operational policies, clear definition of responsibilities, and a continuum of services. The increase in serious crimes by juveniles has produced many reactionary recommendations which may negate progressive measures, such as the development of community-based facilities as a substitute for institutional care. Possible developments include a lowering of the minimum age at which a youthful offender can be prosecuted as an adult criminal and the return or maintenance of a network of large, more restrictive institutions. Efforts to change laws in these directions are under way in many States. Tables, notes, and 50 references are provided.