The data came from a multi-wave panel study that examined the development of delinquent behavior and drug use in a high-risk, urban sample. The initial sample consisted of 1,000 students in the 7th and 8th grades of public schools in Rochester, N.Y., during the 1987-88 academic year. Each adolescent and his or her parent were interviewed at 6-month interviews over a 4.5-year period and again once a year for 3 years following a 2.5-year gap. Data also came from school, police, court, and social service agency records. Results were consistent with most prior research and revealed that males who reported the onset of delinquent behavior prior to age 11 were more likely to offend and to be more frequent, persistent, serious, and wide-ranging offenders than were those who started offending after the elementary school years. Delinquency was generally lower in every category for those who were in the latest-onset group. Findings indicated the need for programs of early identification and referral to prevention services, although little systematic data exists reading the role of early intervention programs for young delinquents. The research on these issues will continue. Figure, tables, and 25 references