Although the US health care system is often touted as one of the best in the world, disparities exist in quality of care received by different populations, in different regions, and across different institutions and clinicians. Initiatives to provide access to health insurance have been a major policy tool to ensure that Americans receive high-quality health care. However, availability of insurance coverage does not automatically lead to high-quality care. This article explores points of vulnerability in the US health care system at which the potential to achieve high-quality care can be lost: (1) access to insurance coverage; (2) enrollment in available insurance plans; (3) access to covered services, clinicians, and health care institutions; (4) choice of plans, clinicians, and health care institutions; (5) access to a consistent source of primary care; (6) access to referral services; and (7) delivery of high-quality health care services. Ensuring high-quality health care requires that each of these "voltage drops" be recognized and addressed. JAMA. 2000;284:2100-2107.