For this 1978 report, the total data base contained more than 515,000 case records collected from 13 States and 2 large jurisdictions; in addition, summary data on 225,000 cases were collected from 7 States and 2 large jurisdictions. The total sample used to generate national estimates included data from 1,317 of the nation's 3,143 counties, representing 53 percent of the total child population subject to the jurisdiction of the Nation's juvenile courts in 1978. For 1978, the child population at risk (defined as the number of children from age 10 to the upper age of juvenile court jurisdiction) was estimated at 28,964,000. For that year, this population produced an estimated 1,340,7000 cases processed by courts with juvenile jurisdiction, or 46.29 cases per 1,000 child population at risk. The estimated number of cases handled by the courts decreased each year between 1975 and 1978, as did the child population, with the rate of delinquency (defined as the number of estimated cases per 1,000 child population at risk) remaning constant. The average case rate from 1975 to 1978 was 46.03 cases per 1,000 child population at risk. While some individual courts may experience an increase, projections indicate that the total number of dispositions handled nationally by courts with juvenile jurisdiction will decrease yearly, an outcome which will have a major impact on the juvenile justice system. Another significant finding was that rates of detention declined over these 4 years, with the greatest decrease in the rate of juveniles referred for status offenses. in 1975, 43 percent of all status offenders were detained; in 1978, only 15 percent of all status offenders were detained. This report, the fourth in an annual series, has been greatly expanded to include an executive summary and detailed explanations of the methodology and findings, supplemented by 21 graphic illustrations. Thirteen univariate tables and 100 bivariate tables are presented, and a glossary of terms is included to aid in defining relevant terminology.