The analyses are based on the Medicaid Quality Control (QC) data base for the first half of 1994, with additional information about Supplemental Security Income (SSI) participants from the Social Security Administration (SSA). The QC data base includes verified data about 93,000 sampled Medicaid enrollees, roughly 2,000 per state, making it the largest known national sample of Medicaid beneficiaries. QC data include relatively detailed information about immigration status, as well as medical expenditures paid by Medicaid in the sample month. The QC sample represents the great majority of Medicaid beneficiaries, but in 31 states the QC sample excludes SSI recipients. Thus, SSA data are used to supplement information about elderly and disabled immigrants, although these data are more limited. Estimates of the number and costs of aged, blind and disabled Medicaid beneficiaries who are noncitizens were generated by combining QC and SSA data.