Criminality trends were measured by the percent of Part I crimes attributable to each age group and by age group crime rates. The former measure gauged the relative criminal involvement of various age groups, and the latter measure determined age group criminality for each year, controlling for the effects of population changes. Crime grew from 1963 to 1983 because of a growth in criminal tendencies across all ages, not just among the juvenile population. The percentage of juveniles who committed violent crimes increased more than did the percentage of adults committing such crimes, but growth in property crime rates was approximately the same across all ages. Changes in age composition exerted small and gradual effects on crime trends over the 20-year period. Changes in criminal propensities accounted for the majority of growth in serious crime. The study also examined trends in social indicators often associated with crime: education, the risk of imprisonment, employment, drug abuse, and family stability. Tabular data, 17 notes, and 9 references.