There is a substantial increase in the number of deaths in winter in the United Kingdom. This is also seen in some, but not all, European countries. Almost 60% of the variation among countries can be explained by the minimum average monthly temperature and the gross national product per capita. Seasonal variation is lowest in those countries with cold winters, suggesting that insulation may be important. It is also low in the more wealthy countries. The implications for health service policy of these finding are discussed. Some of the residual variation may be explained by known factors, such as low cost geo-thermal energy in Iceland, but much remains unexplained. There is a need for more research in this field.