[영문]AB Background: Despite the increasing enrollment of adult disabled beneficiaries into Medicaid managed care organizations (MCOs), there is little evidence of its (hoped for) effectiveness at reducing Medicaid expenditures. Objective: To evaluate the impact of Medicaid MCOs on health care expenditures for adults with disabilities. Research Design: I employ a repeated observations design comparing individual monthly Medicaid expenditures across beneficiaries who reside in counties with mandatory, voluntary, and no MCOs. County-level Medicaid MCO program status for adults with disabilities was merged with the Medical Expenditure Panel Survey and the Area Resource File for 1996-2004. Two-part regression models are used to estimate the probability and level of Medicaid expenditure. Subjects: Working age Medicaid beneficiaries who receive Supplement Security Income for disability comprise the sample of 1613 individuals. Measures: Outcome measures include total and service-specific Medicaid expenditures. Results: On average, total monthly Medicaid expenditures per beneficiary do not differ between FFS and MCO counties although some service-specific spending differs. Relative to FFS counties, average monthly Medicaid spending per beneficiary is higher for prescription medications in voluntary (