When workers with disabilities “buy into” Medicaid by paying monthly premiums, states can offer them Medicaid coverage when their income and assets would otherwise make them ineligible. Using MAX data and Medicare claims files, this report provides the most comprehensive information to date on patterns of Medicaid and Medicare spending and service use among Medicaid Buy-In participants. Researchers found that combined inflation-adjusted Medicaid and Medicare expenditures for Buy-In participants more than doubled from $887 million to $1.9 billion between 2002 and 2005, as did program enrollment. However, they also found that, when compared with other working-age disabled Medicaid enrollees, Buy-In participants in 2005 incurred lower annual Medicaid expenditures. This difference suggests that Buy-In participants who are working may require fewer services or a less expensive mix of services than other adult disabled Medicaid enrollees.