In response to rising numbers of opioid overdose deaths, primary care providers have been called on to play a greater role in delivering buprenorphine treatment for opioid use disorder. However, policy makers and providers have raised concerns that expanding treatment access may reduce treatment quality and that primary care providers are not well equipped to deliver buprenorphine treatment. We investigated two research questions in response to these concerns: How did buprenorphine treatment use and quality change in North Carolina Medicaid from 2014 to 2017, and how did buprenorphine treatment quality differ between primary care providers and specialists in North Carolina Medicaid during this period? We measured buprenorphine treatment quality as patients' retention in treatment and providers' adherence to treatment guidelines. We found that the number of enrollees receiving medication treatment for opioid use disorder increased substantially, but the percentage of enrollees with the disorder receiving treatment remained low. The quality of buprenorphine treatment increased during the study period, and primary care providers provided care of comparable or higher quality compared with that of other providers. Treatment quality for buprenorphine treatment is improving, but there remains room for improvement in both use and quality. Our results support the role of primary care providers in expanding treatment for opioid use disorder.