It is generally acknowledged that adapting low-lying, flood-prone deltas to the projected impacts of climate change is of great importance. Deltas are densely populated and often subject to high risk. Climate-proof planning is, however, not only a new but also a highly complex task that poses problems for existing institutional and administrative structures, which are the product of times in which climate issues were of little importance. This paper assesses the capacity of the historically grown Dutch planning institutions to promote climate-proof planning for flood-prone areas. The Adaptive Capacity Wheel provides the methodological framework. The analysis focuses on two planning projects in the west of the Netherlands: the Zuidplas Polder project at the regional level and the Westergouwe project at the local level. It is shown that the planning institutions involved in these projects enable climate-proof planning, but to a limited extent. They face five institutional weaknesses that may cause risks on the long term. To climate-proof urban developments in flood-prone areas, it is necessary to break through the strong path-dependent development of planning institutions and to build in more flexibility in existing rules and procedures.