In temperate climates, mortality is higher in the winter than the summer. Most wintertime deaths are attributed to cardiovascular and respiratory disease, with hypothermia from extreme cold accounting for a negligible share of all recorded deaths. International and national assessments of the health risks of climate change often conclude that increased temperatures from climate change will likely reduce winter mortality. This article examines the support for this hypothesis. We find that although there is a physiological basis for increased cardiovascular and respiratory disease mortality during winter months, the limited evidence suggests cardiovascular disease mortality is only weakly associated with temperature. Although respiratory disease mortality shows a stronger seasonal relationship with colder temperatures, cold alone does not explain infection rates. Further, respiratory disease mortality is a relatively small proportion of winter deaths. Therefore, assuming no changes in acclimatization and the degree to which temperature-related deaths are prevented, climate change may alter the balance of deaths between winters and summers, but is unlikely to dramatically reduce overall winter mortality rates.due to extreme temperature events that more deaths occur in temperate regions in the winter, generally defined as the three coldest months of the year, is well documented. 5,6 The question is how much of this seasonal variation is directly dependent on temperature versus other factors that vary with the seasons.This article explores the nature and evidence of the relationship between daily mortality, cold spells, and the cold season by first discussing the health impacts of cold temperatures and differentiating between mortality due to cold spells and general winter mortality. We then explore the evidence for the assumption that elevated winter mortality is due directly to temperature to draw conclusions regarding how the balance of hot-and cold-temperature-related mortality could be affected by a changing climate.