Outsourcing can be defi ned as the delivery of public services by the private sector. The sign of the effect of outsourcing on public spending is ambiguous ex-ante. While outsourcing may reduce public spending through higher competition in the private sector, it may also increase public spending due to the presence of transaction costs or the so-called "hold-up" problem among others. Using a panel of Spanish regions over the 2002-2018 period, this paper explores the association between outsourcing and public spending empirically. Spain offers an interesting case study from a broad perspective, as the degree of decentralization of public health and education is almost complete, and the different regions have adopted quite distinct approaches as regards the public-private mix in the provision of these public services.In line with previous cross-country evidence [e.g. Alonso et al. (2017); Potrafke (2018)] our estimates point to a positive relationship between public spending and outsourcing. The result holds when a number of robustness exercises are carried out. By components, we fi nd that outsourcing is associated with higher public consumption and health spending, while there is no statistical association with investment and education expenditure. In any case, it is worth mentioning that the impact of outsourcing on the effi ciency of public spending cannot be ascertained with our approach, due to data limitations.