The effects of climate change on design floods of high hazard dams were studied in Finland. Design floods were calculated with model simulation methods where design precipitation was combined with 40 years of weather data. The combination of design precipitation and baseline weather that produced the largest flood was researched and this flood was used as the design flood of the dam with a return period of 5,000–10,000 years. Design floods were first simulated for the baseline period (1961–2000) and for a future period (2070–2100) and these two floods were compared. The baseline temperatures and precipitations were changed with delta-change approach using five climate scenarios for 2070–2100 and the design precipitation was changed according to two projections. Of the 34 dams included in this study, the effect of climate change varied depending on the location of the dam, the type of the basin and the primary cause of the flood. In northern Finland, where the simulated design floods were mainly caused by spring snowmelt, the design floods did not change significantly. In southern and western Finland, the design floods were mostly summer floods which increased mainly due to the increase in the design precipitation.