Socioeconomic status (SES) has been consistently linked to poorer access, utilization and outcomes of health care services, but this relationship has been understudied in adolescent substance abuse treatment research. This study examined SES differences in adolescent's treatment participation and long-term outcomes of abstinence and 12-step attendance over five years after treatment. Data are from 358 adolescents (ages 13-18) who were recruited at intake to substance abuse treatment between 2000 and 2002 at four Kaiser Permanente Northern California outpatient treatment programs. Follow-up interviews of adolescents and their parents were conducted at 1, 3, and 5 years, with over 80% response rates across time points. Using parent SES as a proxy for adolescent SES, no socioeconomic differences were found in treatment initiation, treatment retention, or long-term abstinence from alcohol or drugs. Parent education, but not parent income, was significantly associated with 12 step attendance post-treatment such that adolescents with higher parent edification were more likely to attend than those with lower parent education. Findings suggest a lack of socioeconomic disparities in substance abuse treatment participation in adolescence, but potential disparities in post-treatment 12-step attendance during the transition from adolescence to young adulthood. (C) 2017 Elsevier Ltd. All rights reserved.