This study examines the impacts of climate change on future mortality in the Netherlands and the related economic costs. Our methods account for changes in both cold- and heat-related mortality for different age classes, the time dynamics associated with temperature-related mortality, demographic change and the urban heat island effect. Results show that heat and cold impacts on mortality vary considerably between age classes, with older people being more vulnerable to temperature extremes. The sensitivity of mortality to temperature is higher on hot (4.6%/°C) than cold (2.1%/°C) days for the most vulnerable group (≥ 80 years), and extreme temperatures have long time lags on mortality, especially in the cold. A main finding is that climate change is expected to first decrease total net mortality in the Netherlands due to a dominant effect of less cold-related mortality, but this reverses over time under high warming scenarios, unless additional adaptation measures are taken. The economic valuation of these total net mortality changes indicates that climate change will result in net benefits of up to €2.3 billion using the Value of a Statistical Life Year and €14.5 billion using the Value of a Statistical Life approaches in 2050, while this changes over time in net economic costs under high warming scenarios that can reach up to €17.6 billion in 2085. Implementing adaptation policies that reduce the negative impacts of warming on mortality in the heat can turn these net costs into net benefits by achieving a continued dominating effect of reduced mortality in the cold.