Despite continuous efforts to improve, the construction industry is prone to failure of large infrastructure projects in terms of time and cost overruns. It is believed good interface management is contributing to the success of infrastructure projects. The research has been executed at Heijmans, a major contractor in the Netherlands. The purpose of this research is to explore which organizational interfaces are related to project success, from a contractor's perspective, and how this can be improved. In order to assess which organizational interfaces are present on infrastructure projects an exploratory case study of four road infrastructure projects with integrated contracts, has been performed. Current literature shows that the definition of project success is different for each stakeholder on the project. Clients are mainly interested in indicators related to the outcome of the project. End users find a project successful when it meets their expecations. Contractors continue to value indicators related to costs, time and quality, most important. The research identified a number of organizational interfaces present on road infrastructure projects with integrated contracts at Heijmans, namely internal relations within Heijmans, the relation with the client and the relations with subcontractors. The case study has revealed there is a difference with respect to client type. In general, projects in cooperation with Rijkswaterstaat were more successful in comparison to projects with lower government organizations. The root cause for this difference in relationship is the level of knowledge and experience from the client. This difference results in controlling behaviour from the client which frustrates the process for the contractor, resulting in less control and lower project success. A good relationship between client and contractor is essential for project success.