Past research has shown that a relatively small number of youths are responsible for a large proportion of the offenses committed by juveniles, leading juvenile justice practitioners to ask what the courts can do to intervene early to deter these youth from committing further serious delinquent acts. To answer this question, a research study was undertaken to examine, from the court's perspective, the delinquent careers of chronic juvenile offenders. The research involved the analysis of the court career and offense patterns of nearly 70,000 youth in Phoenix, Arizona and the state of Utah. The findings suggest that juvenile courts have an opportunity to intervene in the lives of a large percentage of youth at a time when problems are apparent and also have the authority to effect change. The finding that a youth referred to court for a second time before the age of 16 could, with a high degree of certainty, be considered a chronic offender implies that the courts should not wait until the youth has returned for the fourth or fifth time before taking strong action. This report describes the research conducted in Arizona and Utah and the findings revealed. Chapter 1 discusses the need for court career research. Chapter 2 explains the sources of juvenile court career data. Chapter 3 describes youth with juvenile court careers; chapter 4 explores the development of juvenile court careers; and chapter 5 characterizes juvenile court career types. Chapter 6 presents a summary and conclusions. The appendix explains the recoding of offense codes into reporting codes. Numerous tables display the statistical data. (NB)