Aged Medicare beneficiaries are a minority of Medicaid enrollees but are disproportionately expensive largely because of their greater for need long-term services and supports. High out-of-pocket costs of care, especially nursing home care, may result in transition to Medicaid when private resources are insufficient. This study provides new estimates the prevalence and predictors of Medicaid enrollment in the older population, using multiple years of Medicaid and other administrative data linked to the 2004 National Long-Term Care Survey. Estimates indicate that 5% of community-residing Medicare beneficiaries will transition within 4 years. Findings do not indicate widespread middle class access to Medicaid. Nursing home entry was by far the largest predictor of transition, followed by low income and assets, consistent with Medicaid’s stringent financial eligibility standards. In the lowest income group, 30% of nursing home users but only 6% of nonusers transitioned to Medicaid.