Recent movements to deprofessionalize American state legislatures have been driven partly by the notion that professional legislators spend more than their citizen counterparts. This article explores the relationship between legislative professionalism and government spending, a connection complicated by the possibility that legislators in high-spending states may choose professional institutions to handle their responsibilities more effectively. I employed propensity score matching, an increasingly used technique of causal inference, to disentangle the relationship. Contrary to previous academic work and popular notions, I found that professional legislatures do not spend significantly more than part-time bodies do, if one accounts for the fact that legislatures in high-spending states have a greater need to be professionalized and therefore select those structural frameworks. These findings have important implications for the study of the effects of legislative institutions on public policies more generally and attest to the utility of recently developed techniques of causal inference to disentangle these relationships.