The first cohort consisted of 9,945 males born in 1945 and who lived in Philadelphia at least from age 10 to 18; 7,043 were white and 2,902 were nonwhite, and 28.64 percent of whites and 50.24 percent of nonwhites were delinquent. An examination of persistent offenders, those who committed offenses during both juvenile and adult periods, showed that the relationship between race and offender status was pronounced and significant. In general, offense careers of nonwhite subjects were more likely to persist over both juvenile and adult years, whereas whites were more likely to be juvenile delinquents only. In terms of the frequency of violations, juvenile and adult offenders were similar. Persistent offenders, however, committed far more offenses and committed the most serious offenses. The second cohort included 13,160 males and 14,000 females born in 1958 who, like the first cohort, lived in Philadelphia at least from age 10 to 18. Of 6,216 white males in this cohort, 1,412 (23 percent) were recorded as delinquent by the police before age 18; of 6,944 nonwhite males, 2,903 (42 percent) were delinquent. Nearly a third of male subjects experienced at least one officially recorded police contact by age 28. Overall, 9.8 percent of cohort males were arrested only as adults, 18.8 percent only as juveniles, and 13.6 percen both as juveniles and as adults. In contrast, 85.9 percent of cohort females never experienced police contacts during their childhood years, and only 2.5 percent were arrested as adults. Females who had adult arrest records were also likely to have had juvenile police records, even though they represented only 3.9 percent of the female population. As in the first cohort, significant racial differences were observed in recorded prevalence rates for juvenile and adult criminal behavior. 5 references, 1 note, and 11 tables