In collaborative efforts three research teams have investigated the problems of urban delinquency and substance abuse in longitudinal studies that have gone on since 1986. The Denver Youth Study is a longitudinal survey that involves annual interviews with probability samples of five different birth cohorts and their parents from areas of Denver (Colorado) that display high risk for delinquency. The Pittsburgh Youth Study, in two phases, selected boys attending grades 1, 4, and 7 in Pittsburgh (Pennsylvania) public schools. Of 2,250 initial subjects, 1,500 have been selected for followup. The Rochester Youth Development Study started with a sample of 1,000 boys and girls in Rochester (New York) and collected data on them over 4.5 years. This report updates an earlier report on these three studies, published in 1994, and supports previous conclusions. Violent offenses increased markedly with the onset of drug use, as did the carrying of concealed weapons. Continued drug use has been associated with an increase in violent offenses and the frequency of carrying weapons. The onset of drug selling for these juveniles was associated with an increase in violent crime, and the percentage of drug dealers carrying guns rose steadily for those between the ages of 16 and 19. When drug use was discontinued, violent offenses decreased. Findings are grouped into the following sections: (1) "Introduction"; (2) "Results: Delinquency and Drug Use"; (3) "Results: Overlap of Problem Behaviors"; (4) "Results: Explanatory Factors and Delinquency"; (5) "Results: Common Themes"; and (6) "Programmatic Implications." (Contains 1 table and 15 figures.) (SLD)