States increasingly use managed care for Medicaid enrollees, yet evidence of its impact on health care outcomes is mixed. This research studies county-level Medicaid managed care (MMC) penetration and health care outcomes among nonelderly disabled and nondisabled enrollees. Results for nondisabled adults show that increased penetration is associated with increased probability of an emergency department visit, difficulty seeing a specialist, and unmet need for prescription drugs, and is not associated with reduced expenditures. We find no association between penetration and health care outcomes for disabled adults. This suggests that the primary gains from MMC may be administrative simplicity and budget predictability for states rather than reduced expenditures or improved access for individuals.