One hundred youths in a typical American city were selected as representative of all youths, delinquent drug users in the community, and officially labeled delinquents. Youths were intensively interviewed (average 5 hours), and transcripts of the interviews were qualitatively analyzed. Seriously delinquent youths reported regular use of drugs and alcohol. Although such delinquent youths believe that drug and alcohol use may indirectly cause other youths to commit crimes, they do not perceive such a connection in their own crimes. They admit to committing theft to obtain money or goods, but they do not relate this to drug use. The youths report selecting which substances to use or avoid before a crime. Delinquents select victims who are careless about protecting their property, and they limit aggressive crimes to only a few contexts. Drug sellers are among the most frequent users of drugs and alcohol. They consume most of their profits and limit their sales to people they know and to private places. At approximately age 16, many delinquents reduce their criminality and voice concern about the harsher sanctions they would receive as adult offenders. Four case studies describe life processes among seriously delinquent drug users and 13-year-olds at risk for future involvement in drugs and delinquency. 9 tables, 265 references, and appended interview schedule and data processing items (Author abstract modified)