The United States invests a sizable amount of money on treatments for mental health and substance abuse: $135 billion in 2005, or 1.07 percent of the gross domestic product. We provide treatment spending estimates from the period 1986-2005 to build understanding of past trends and consider future possibilities. We find that the growth rate in spending on mental health medications-a major driver of mental health expenditures in prior years-declined dramatically. As a result, mental health and substance abuse spending grew at a slightly slower rate than gross domestic product in 2004 and 2005, and it continued to shrink as a share of all health spending. Of note, we also find that Medicaid's share of total spending on mental health grew from 17 percent in 1986 to 27 percent in 2002 to 28 percent in 2005. The recent recession, the full implementation of federal parity law, and such health reform-related actions as the planned expansion of Medicaid all have the potential to improve access to mental health and substance abuse treatment and to alter spending patterns further. Our spending estimates provide an important context for evaluating the effect of those policies.