Résumé : Several national health systems in Latin America initiated health reforms to counter widespread criticisms of low equity and efficiency. For public purchasing agencies, these reforms often consisted in contracting external providers for primary care provision. This paper intends to clarify both the complex and intertwined issues characterizing such contracting as well as health system performances within the context of four Central American countries. It results from a European Commission financed project lead between 2002 and 2005, involving participants from Costa Rica, Guatemala, Nicaragua, Salvador, United Kingdom, Netherlands and Belgium, whose aim was to promote exchanges between these participants. The findings presented in this paper are the results of a two stage process: (a) the design of an initial analytical framework, built upon findings from the literature, interlinking characteristics of contractual relation with health systems performances criteria and (b) the use of that framework in four case studies to identify cross-cutting issues. This paper reinforces two pivotal findings: (a) contracting requires not only technical, but also political choices and (b) it cannot be considered as a mechanical process. The unpredictability of its evolution requires a flexible and reactive approach. This should be better assimilated by national and international organizations involved in health services provision, so as to progressively come out of dogmatic approaches in deciding to initiate contractual relation with external providers for primary care provision. © 2008 Elsevier Ireland Ltd. All rights reserved.