Inter-institutional cooperation between the congress and the presidency may be the best way to promote good governance in a regime of separation of powers. In order to evaluate the performance of different political institutions, especially the different frameworks associated with ‘presidentialism’ and ‘parliamentarism’, we adopt the criterion that policy outcomes coinciding with the median voter's preference can produce the highest satisfaction or social utility. From this perspective, proportional representation in congress can be very appropriate since it tends to establish a close correspondence between the median party's and the median voter's preferences. Likewise, cooperation – rather than conflict or mutual checks – between the median party in congress and the presidency for both legislative decisions and cabinet formation can favour socially efficient outcomes. A survey of some recent institutional reforms in democratic presidential regimes in Latin America shows that ‘parliamentarization’ of presidentialism is gaining acceptance, although intermediate formulae may be more conflictual than a global, more coherent institutional reform.