Academic debate in South America favours a MERCOSUR monetary union based on the euro and the Economic and Monetary Union (EMU), and inspired by the theory of Optimal Currency Area (OCA). This paper aims to discuss whether the adoption of a single currency in the EMU mould of monetary union, is appropriate and feasible for the MERCOSUR. Three lessons are derived for MERCOSUR from the euro and the EMU experience: the adoption of the EMU model of monetary union would imply deflationary policies; there is the dilemma of sequencing between political union and economic integration; and the necessity of accounting seriously the concerns of the OCA literature. The paper also shows that there is no evidence that macroeconomic convergence is evident in MERCOSUR, since the area only minimally achieved some basic criteria defined by the OCA literature.