This study examined correlates of methamphetamine (MA) and marijuana (MJ) use and treatment response among treatment-involved youth (N = 4,430) in Los Angeles County, California treated between 2000 and 2005. Of the sample, 912 (21%) were primary MA and 3,518 (79%) were primary MJ users. Correlates of increased MA use included being female, White, Asian or Latino, older age, previous treatment involvement, legal status of probation or parole, and initiating drug use at an older age. Treatment trends showed a rise in treatment admissions for MA, with more MA users enrolling in residential treatment compared to outpatient treatment. Predictors of retention, drug use at discharge, and completion by treatment modality are discussed. Results can guide the development of effective strategies for treatment assessment and planning tailored towards minimizing drug use and maximizing treatment response among youth. (Contains 2 tables.)