This study uses longitudinal data to examine the consequences of losing and gaining health insurance coverage for access to care and health. For both Medicaid and privately insured persons, compared with those who remained insured, persons losing coverage over a 2-year period were more likely to lack a usual source of care, encounter difficulty in obtaining medical care, be very dissatisfied with ability to obtain needed care, and report no physician visits in the previous 12 months. Uninsured people who gained coverage showed improvement across all indicators of access, in contrast to those who remained without insurance. The effects of changes in coverage on health were in the same direction as those for access, but did not reach statistical significance. This study strengthens the evidence that health insurance coverage has a substantial impact on ability to gain access to medical care and may affect health status.