Highlights of findings include: (1) in 2006, repeat admissions aged 18 to 25 were more likely than first-time admissions aged 18 to 25 to report heroin and other opiates as the primary substance of abuse (27 percent versus 12 percent) and to report the use of multiple substances (67 percent versus 56 percent); (2) the South was unlike any other region in that a majority of all admissions aged 18 to 25 were first-time admissions instead of repeat admissions, regardless of the primary substance of abuse; and (3) the criminal justice system was the principal referral source to substance abuse treatment for both 18 to 25 year-old repeat admissions (46 percent) and first-time admissions (52 percent). Relapse to substance use after a period of abstinence is a common pattern among substance abusers. Many are admitted to substance abuse treatment multiple times before they achieve long-term abstinence. First-time and repeat admissions can be examined with information from the Treatment Episode Data Set (TEDS), an annual compilation of data on the demographic characteristics and substance abuse problems of those admitted to substance abuse treatment, primarily at facilities that receive some public funding. In 2006, nearly a quarter (22 percent) of all admissions to substance abuse treatment were aged 18 to 25. This report compares the characteristics of first-time admissions aged 18 to 25 with repeat admissions of the same age and seeks to provide additional insight into the distinct characteristics of admissions that have had multiple encounters with the substance abuse treatment system. Tables, figures, and notes