Adverse childhood experiences (ACE) are a public health concern and strong predictor of substance abuse, but no studies to date have explored the association between ACE and opioid relapse during medication-assisted treatment. Using an observational design, we examined this relationship using archived medical records of 87 patients who attended opioid use disorder treatment (buprenorphine-naloxone and group counseling) at a rural medical clinic. All variables were collected from medical files. ACE scores were derived from a 10-item screening questionnaire administered at intake, a regular procedure for this clinic. The primary outcome was opioid relapse observed at each visit, as indicated by self-reported opioid use, positive urine drug screen for opioids, or prescription drug database results for opioid acquisition. The sample was 100% Caucasian and 75% male. A total of 2052 visit observations from the 87 patients were extracted from the medical records. Patients had an average of 23.6 (SD = 22) treatment visits. Opioid relapse occurred in 54% of patients. Results indicated that for every unit increase in ACE score, there was an increase of 17% in the odds of relapse (95% CI: 1.05–1.30, p = .005). Additionally, each treatment visit was associated with a 2% reduction in the odds of opioid relapse (95% CI: 0.97–0.99, p = .008). We conclude that ACE may increase the risk for poor response to buprenorphine-naloxone treatment due to high rates of opioid relapse during the first treatment visits. However, consistent adherence to treatment is likely to reduce the odds of opioid relapse.