IMPORTANCEDisruptions in care during the COVID-19 pandemic may have decreased access to care for patients with opioid use disorder. OBJECTIVE To examine trends in opioid use disorder treatment including buprenorphine possession, urine drug testing, and opioid treatment program services during the COVID-19 public health emergency. DESIGN, SETTING, AND PARTICIPANTS This cohort study included 6453 parent and childless adult Medicaid beneficiaries, aged 18 to 64 years, with opioid use disorder and continuous enrollment from December 1, 2018, to September 30, 2020, in Wisconsin. Logistic regression compared differences in study outcomes before, early, and later in the COVID-19 public health emergency. Analyses were