The cohorts included 6,127 persons, of whom 4,079 lived continuously in Racine from at least age 6 until the cutoff dates of 1974 for the first two cohorts and 1976 for the third cohort. Interview data from 889 subjects from the 1942 and 1949 cohorts and data on police contacts, referrals, and court dispositions for all the subjects were analyzed. Comparison of the three cohorts showed that overall rates of contact with the police did not increase from cohort to cohort as much as did rates of police contact for the more serious offenses such as assault, burglary, theft, and robbery. Delinquency among females increased even more than it did among males. However, changes in police administrative and recording procedures probably caused part of the increase in contacts. Although police contacts were widespread among juveniles, few developed adult criminal careers. Police contacts and more serious contacts were concentrated in the inner city and related areas. A small proportion of the population was continuously and seriously involved with the police throughout their lives. The seriousness of their crimes gradually increased from contact to contact among males, although the progression was not systematic. The significant effect of juvenile crime seriousness on adult crime seriousness persisted even when the intervening effects of juvenile referrals and sanctions were held constant. Data indicated that to reduce delinquency rates and such continuities between juvenile and adult crime as do exist, steps must be taken to modify the operation of community institutions, including the school system, police forces, and the system under which sanctions are applied. Procedural and institutional changes suggested by the findings are described. Extensive tables, charts, graphs, appendixes presenting study instruments and additional findings, and about 300 references are provided.