Abstract Climate adaptation planning in pursuit of resilient and sustainable societies has become a focal point in urban policy. Climate adaptation planning is generally regarded as separate from traditional urban planning practices. Globally and in Europe, however, cities are increasingly integrating climate adaptation planning into their traditional urban planning instruments and processes. Recent research indicates that the scope of such integration is at varying stages. The City of Rotterdam (Netherlands) and the City of Antwerp (Belgium) have been identified as two European cities that face similar climate impacts and risks given their proximity to a large river delta. Both cities aim to integrate climate adaptation into their respective urban planning policies, but the scope of their integration differs. This paper critically analyses the urban planning policies of these two cities to distil key lessons learnt that cities with similar climate impacts and approaches to urban planning may potentially face in integrating climate adaptation planning into urban planning policies. The paper finds that identifying and evaluating the synergies, co-benefits or trade-offs of adaptation measures is a key challenge to integrating climate adaptation into urban planning policy. It is a potential stumbling block for long-term sustainable development and climate resilience.