This short paper presents the approach which has been implemented in France for estimating the costs of ecosystem degradation in the context of the Marine Strategy Framework Directive (MSFD). Among the possible approaches, forgone benefits assessment or maintenance costs assessment, France decided to use the latter. The paper contains an introduction, a section which explains how to choose an economic approach coherent with the MSFD rationale, a section which exposes the methodology developed for implementing the approach, and a section on the main results.