Dike reinforcement decision making under uncertainty is a challenging task. This paper examines whether increasing the managerial flexibility of a reinforcement strategy can improve the lifecycle cost-effectiveness for the Dutch flood defences. Two flexible strategies are developed and compared to an inflexible baseline strategy. The strategies are examined in eight case studies, two sea level rise scenarios, and four discount rates. It is shown that increasing the flexibility of reinforcement can improve the cost-effectiveness for monofunctional dikes. The relative cost-effectiveness of flexible strategies decreases as the dike becomes multifunctional. The results prove to be sensitive to the choice of the scenario and discount rate. It is concluded that reinforcement decision making should address uncertainty explicitly and account for smaller scale developments around the dike. It is suggested that current engineering practice can be improved if the possibility of a variable design lifetime is also addressed in reinforcement decision making.