Medicaid managed care insurers play a crucial role in facilitating access to buprenorphine to treat opioid use disorder. Using a novel set of provider directory and prescription claims data, we examined variation in access to in-network buprenorphine-prescribing primary care providers among Medicaid managed care enrollees. Approximately 32.2 percent of enrollees had fewer than one in-network buprenorphine prescriber per 100,000 county residents. On average, there were a greater number of in-network buprenorphine-prescribing primary care providers in states with higher compared with lower overdose death rates. However, most enrollees lived in areas with a shortage of these providers. We found that a 25 percent higher network participation rate by prescribers compared with nonprescribers could improve the probability that enrollees see a prescriber by approximately 25 percent. Policies to improve access within Medicaid managed care include using primary care provider assignment algorithms to match patients with buprenorphine prescribers and requiring that networks include a minimum number of buprenorphine prescribers.