Two-thirds of the sample are male, 93 percent are white, and their mean age is 15.9 years. Of subjects, 81 percent are still in school, 42 percent live with both biological or adoptive parents, and 46 percent live with a single parent. The majority of adolescents reported problems other than substance abuse, including learning disabilities, behavioral problems, affective disorders, sexual or physical abuse histories, low self-esteem, and relationship problems. A majority have parents who also abuse substances. Over half had been expelled or suspended from school, 55 percent have been arrested, and over 25 percent have been in treatment before. Half of the population began drinking by age 12, smoking marijuana by 13, and using other drugs by 14. Marijuana was the most frequently used substance, with 48 percent using it daily. Chemical dependency symptom are extensive, 81 percent consider themselves dependent. Over two-thirds completed treatment, with girls being more likely than boys to complete treatment. Of 915 subjects out of treatment for a year, 493 could be followed up. Of these, 44 percent reported total abstinence of all mood-altering drugs, 22 percent reported at least 3 months' abstinence during both 6-month followup periods, and 35 percent reported prolonged or multiple relapses. Being female, treatment completion, and participation in support groups were significantly associated with post-treatment sobriety. 33 tables.