Following successful deployment in the aerospace and automotive industries, the demand for a structured approach to Systems Engineering on large infrastructure projects is rapidly increasing in the current decade. However, there is still certain inertia on the part of some firms to adapt their processes within this engineering discipline, and hence an empirical demonstration of the benefits of systems engineering is needed. The purpose of this paper is twofold: on the one hand, it outlines an overall methodology to perform studies on Return on Investment of Systems Engineering (SE-ROI) in large infrastructure engineering companies; on the other hand, this paper presents the results of this methodology applied to calculate the SE-ROI in one such infrastructure engineering company.