This analysis was restricted to relatively serious violent crimes, namely, aggravated assault, robbery, and forcible rape. Both the Uniform Crime Reports (offenses known to police) and the NCVS (reports by victims of the offenses in which the offender was known to be a juvenile) showed that there were decreases in serious violent offending by juveniles until about 1986-87 and increases thereafter until about 1994, when sharp decreases began and continued until 1998. Both race and gender disproportionately declined between 1980 and 1998, both in the Uniform Crime Reports and NCVS data, as the overrepresentation of male offenders and the overrepresentation of Black offenders decreased. The data from the NCVS showed that the majority of juvenile violent offending was done in groups, with male juveniles being more disposed to group offending than female juveniles and Black juveniles much more than white juveniles. The declines in juvenile offending rates for serious violent crimes between 1994 and 1998 were greatest for juvenile co-offending, especially for Blacks. Possible explanations for this dramatic decrease in violent co-offending among Black juveniles should be explored, so as to enhance understanding of the recent decline in overall crime, with attention to the disparate declines in lone and group offending. 14 figures, 9 notes, and 17 references