Although people will most likely adjust to warmer temperatures, it is still difficult to assess what this adaptation will look like. This scenario-based integrated health impacts assessment explores baseline (1981–2010) and future (2050) population attributable fractions (PAF) of mortality due to heat (PAFheat) and cold (PAFcold), by combining observed temperature–mortality relationships with the Dutch KNMI’14 climate scenarios and three adaptation scenarios. The 2050 model results without adaptation reveal a decrease in PAFcold (8.90% at baseline; 6.56%–7.85% in 2050) that outweighs the increase in PAFheat (1.15% at baseline; 1.66%–2.52% in 2050). When the 2050 model runs applying the different adaptation scenarios are considered as well, however, the PAFheat ranges between 0.94% and 2.52% and the PAFcold between 6.56% and 9.85%. Hence, PAFheat and PAFcold can decrease as well as increase in view of climate change (depending on the adaptation scenario). The associated annual mortality burdens in 2050—accounting for both the increasing temperatures and mortality trend—show that heat-related deaths will range between 1879 and 5061 (1511 at baseline) and cold-related deaths between 13,149 and 19,753 (11,727 at baseline). Our results clearly illustrate that model outcomes are not only highly dependent on climate scenarios, but also on adaptation assumptions. Hence, a better understanding of (the impact of various) plausible adaptation scenarios is required to advance future integrated health impact assessments.