Objective: To qualitatively explore how treatment-involved youth retrospectively contextualize relapse from substance use. Methods: Fourteen focus groups were conducted with 118 youth (78.3% male; 66.1% Latino) enrolled in participating substance abuse treatment programs (4 young adult and 10 adolescent) throughout Los Angeles County. Transcripts were analyzed for relapse perception themes. Results: Dominant relapse themes include emotional reasons (90%), life stressors (85%), cognitive factors (75%), socialization processes (65%), and environmental issues (55%). Conclusions: Youth perceptions about relapse during treatment should be used to better inform clinical approaches and shape early-intervention recovery agendas for substance-abusing youth.