This study used Medicaid Analytic eXtract (MAX) files to develop national estimates of Medicaid substance abuse (SA) treatment spending, as well as estimates of state spending in 18 states with predominantly fee-for-service coverage of SA treatment. Nationally, medical expenditures to treat SA disorders were $3.4 billion in 2008. About 1.1 million people received services, slightly less than 1 percent of Medicaid enrollees, averaging $3,000 per service user per year. There was extreme variation across states in the average amount spent on SA treatment services per Medicaid enrolled month among individuals age 12 and older, with treatment spending ranging from less than $3 per enrolled month to over $26.