To compare conclusions about delinquency careers derived from court referrals and self-reports, this study analyzed data collected in the Seattle Social Development Project (SSDP), a longitudinal survey of 808 children consenting to the study. Annual court and self-report data were available from age 11 to age 17 for eight offenses. Information was collected from youths, their parents, teachers, school records, and King County (the greater Seattle area), in the fall of 1985, when the youth had a mean age of 10.8, and then in the spring of each year until 1991, and again in spring 1993. There were important similarities and differences between results obtained from the two sources. The prevalence of offending was greater in self-reports than in court referrals, especially for drug offenses. In both court referrals and self-reports, the prevalence of offending generally increased with age. Court referrals and self-reports clearly differed in their conclusions about whether the individual offending frequency varied or stayed constant with age. This frequency stayed constant in court referrals but increased in self-reports. These analyses indicate that criminal career research based on self-reports would yield different theoretical implications from research based on official records. In summation, in self-reports, prevalence and individual offending frequency were higher, the age of onset was earlier, and the continuity and concentration of offending were greater. Self-reports and court referrals agreed in showing that the prevalence of offending increased during the juvenile years and that an early onset predicted a large number of offenses in total. Tables and references