Public-private partnerships (PPP) have become a key tool in the provision and management of transport infrastructure projects providing countries access to the necessary financial resources for infrastructural needs. Despite the increasing number of PPP projects implemented in many countries, there are factors that hinder development of these projects. One of these factors is the weakness of the institutional environment, particularly in developing countries. To date, few empirical studies have analysed the effects of public institutions on PPP projects, despite the relevance of this issue. The objective of this paper is to analyse the influence of institutional environment on the investment carried out through public-private partnerships in middle-and-low income countries for the period 1996-2011. This paper carries out a statistical analysis of the institutional environment indicators, and data of public-private investment, for 80 countries. Our analysis identifies the most relevant institutional factors that affect the implementation of PPP projects.