© 2016 Elsevier Ireland LtdBackground Alcohol and other drug (AOD) use are significant cause of disease burden and costs among adolescents. Methods We conducted a randomized trial in hospital emergency departments (ED) following an AOD-related presentation, comparing usual care with brief advice and referral to link adolescents aged 12–19 years with external AOD services. Subsequently, we used health data linkage to assemble data on mortality, hospital admissions, ED attendances, out-patient mental health and use of opiate pharmacotherapies in the next 10 years. From these, treatment costs and rates of events were estimated and compared using generalized linear models. Results Those who received the intervention had lower costs ($22 versus $227: z = 3.16, p = 0.002) and rates (0.03 versus 0.25: z = 2.57, p = 0.010) of ED mental health AOD presentations. However, the intervention did not significantly reduce overall mean health costs per patient (intervention $58746 versus control $64833, p = 0.800). Similarly, there was no significant difference in the costs associated with hospitalizations ($48920 versus $50911 p = 0.924), overall ED presentations ($4266 versus $4150, p = 0.916), out-patient mental health services ($4494 versus $7717, p = 0.282), or opiate pharmacotherapies ($1013 versus $2054, p = 0.209). Injecting drug use was a significant baseline predictor of subsequent costs in the cohort (z = 2.64, p = 0.008). Conclusions An ED delivered intervention may reduce direct ED costs and subsequent ED AOD attendances. There was also some indication that overall costs may be impacted, with economically large but non-significant differences between the groups. The high costs and morbidity incurred by some of this cohort illustrate the importance of targeting high-risk adolescents.