Youths sent to TYC facilities are the State's most serious or chronically delinquent offenders. This study focused on their behaviors before they began their current TYC commitment. The study addressed the backgrounds and current characteristics of youths in TYC facilities, their patterns of substance use and abuse, and how their substance use and misuse are related to crime. Where appropriate, similarities and distinctions were drawn between girls and boys. Using a random sample, data were obtained from 1,026 youths recently admitted to the TYC intake facility at Marlin, TX. Eighty-one percent of the youths had smoked cigarettes during the year before entering the facility, and 26 percent smoked during the month before incarceration. Seventy-eight percent of the youths drank an alcoholic beverage in the past year, and 21 percent drank in the past month; 13 percent of all TYC offenders were binge drinkers (had five or more drinks on two or more occasions in the past month). Ninety-one percent of TYC offenders had ever used an illicit drug, with 84 percent having used an illicit drug in the past year; and 29 percent used an illicit drug in the past month. Marijuana was the most prevalent drug used in the past year (80 percent), followed by powder cocaine (40 percent), "downers" (31 percent), psychedelics (30 percent), and opiates other than heroin (26 percent). Marijuana was cited by the youths as being the drug that had caused them the most problems. Data are also provided on the youths family backgrounds, including neglect or abuse; parental substance use; education and schooling; HIV risk and risk for pregnancy; children of TYC youth; mental health; and gambling. Data are also presented on criminal behavior and its association with drug use. This report advises that in-facility and follow-up treatment programs should comprehensively address the many social, psychological, and health-related problems associated with the misuse of drugs and alcohol. 14 figures, 77 tables, and appended data on the prevalence and recency of substance use, prevalence and recency of crime, and questions used to create family dynamics indexes