The study explored three areas: the relationship between age and crime seriousness, the effect of age on criminal sanctions, and the degree of information-sharing that occurs between the juvenile courts and criminal courts. A review of other studies shows that late adolescence and early adulthood are critical years in terms of criminality. Most serious adult offenders, particularly those with sustained criminal careers, are in contact with the system at this time. A survey of prosecutors shows that there is considerable variation in the extent to which different jurisdictions have access to and make use of juvenile criminal history information in adult criminal proceedings. Much of the variation appears to be unrelated to the formal legal restrictions placed on the use of such data by State law. In order to study the relationship between age and sanctions, existing data files from three jurisdictions were examined: Los Angeles County, Calif., Franklin County, Ohio; and New York City. In New York, the jurisdiction of the family (juvenile) court ends at the 16th birthdate; in California and Ohio, juvenile status ends at the 18th birthdate. The analysis revealed that the treatment of young adult males varied in several important ways among the three locations. In Los Angeles, young adults were not treated more leniently as measured by their conviction rate, incarceration rate, or State commitment rates, and that 18-year-olds faced a slightly higher risk for any of these outcomes than did older offenders. In Franklin County, young adults were less likely to be incarcerated than older offenders. For New York City, data showed that the youngest age group in the criminal court gets a considerable break. But after age 18, sentence severity remained fairly constant. Finally, a comparison of age-disposition patterns across these three sites points to several conclusions: (1) there is no one national sanction policy for youth; (2) the degree of variation appears to be crime-specific; and (3) variations in sanction severity across sites cannot be readily explained by differences in organization or procedures. Figures, tables, and footnotes are included. A list of 43 references and appended material on juvenile record use in Los Angeles County and legal issues related to accessibility of juvenile records for use in adult court are provided. (Author abstract modified)