Understanding the extent to which beneficiaries can "realize" access to reported provider networks is imperative in mental health care, where there are significant unmet needs. We compared listings of providers in network directories against provider networks empirically constructed from administrative claims among members who were ages sixty-four and younger and enrolled in Oregon's Medicaid managed care organizations between January 1 and December 31, 2018. "In-network" providers were those with any medical claims filed for at least five unique Medicaid beneficiaries enrolled in a given health plan. They included primary care providers, specialty mental health prescribers, and nonprescribing mental health clinicians. Overall, 58.2 percent of network directory listings were "phantom" providers who did not see Medicaid patients, including 67.4 percent of mental health prescribers, 59.0 percent of mental health nonprescribers, and 54.0 percent of primary care providers. Significant discrepancies between the providers listed in directories and those whom enrollees can access suggest that provider network monitoring and enforcement may fall short if based on directory information.