This article argues that the consequences of the ‘fragmentation’ of the European patent system are more dramatic than the mere prohibitive costs of maintaining a patent in force in many jurisdictions. The prevalence of national jurisdictions, which are highly heterogeneous in their costs and practices, over the validity and enforcement of European patents induces both a high level of uncertainty and an intense managerial complexity which undoubtedly reduces both the effectiveness and the attractiveness of the European patent system in its mission to stimulate innovation.