This study examines the association between buprenorphine treatment in emergency departments (EDs) and subsequent engagement in opioid use disorder (OUD) treatment 30 days later. Conducted in seven California EDs participating in a statewide implementation project, the study included 464 patients with OUD. The primary outcome was engagement in OUD treatment 30 days after the ED visit, determined by patient report or clinical documentation. All participants were offered buprenorphine treatment, and the uptake was examined as the exposure of interest. The results showed that 85.8% of patients received buprenorphine treatment, with 58.0% administered in the ED and 73.1% prescribed. At 30 days, 49.7% of those treated with buprenorphine remained engaged in OUD treatment compared to 22.7% of those not treated with buprenorphine. The adjusted risk ratio for engagement was 1.97 (95% CI, 1.27-3.07). The findings suggest that ED buprenorphine treatment is associated with a significantly higher likelihood of follow-up treatment engagement, highlighting the importance of integrating buprenorphine into ED practices to improve patient outcomes. Future research should focus on optimizing the uptake and effectiveness of buprenorphine initiation in low-threshold settings like EDs.This study examines the association between buprenorphine treatment in emergency departments (EDs) and subsequent engagement in opioid use disorder (OUD) treatment 30 days later. Conducted in seven California EDs participating in a statewide implementation project, the study included 464 patients with OUD. The primary outcome was engagement in OUD treatment 30 days after the ED visit, determined by patient report or clinical documentation. All participants were offered buprenorphine treatment, and the uptake was examined as the exposure of interest. The results showed that 85.8% of patients received buprenorphine treatment, with 58.0% administered in the ED and 73.1% prescribed. At 30 days, 49.7% of those treated with buprenorphine remained engaged in OUD treatment compared to 22.7% of those not treated with buprenorphine. The adjusted risk ratio for engagement was 1.97 (95% CI, 1.27-3.07). The findings suggest that ED buprenorphine treatment is associated with a significantly higher likelihood of follow-up treatment engagement, highlighting the importance of integrating buprenorphine into ED practices to improve patient outcomes. Future research should focus on optimizing the uptake and effectiveness of buprenorphine initiation in low-threshold settings like EDs.