This study examined levels, timing, and patterns of posttreatment alcohol and drug use in adolescents (n = 113) during the 12 months following completion of primary treatment. Data were collected from clinical records, random urine screens, and interviews with the adolescents and their parents. In all, 61.1% relapsed to pretreatment levels of use during the 12 months after treatment, 79.6% of the males and 59.3% of the females. Of those with alcohol as the drug of dependence, 45.9% relapsed to pretreatment levels of use in 12 months. Likewise, 75.0% marijuana users, 70.6% combined alcohol and marijuana users, and 50.2% other drug users relapsed to pretreatment levels of use in the 12 months. Relapse curves are presented to demonstrate the specific timing and patterns of relapse. Implications for primary treatment and aftercare are discussed.