Epidemics of influenza are associated with increases in mortality and morbidity.1 Health professionals and the media, therefore, have often focused their attention on influenza as a cause of increased mortality and demands on health services in winter. Cold weather alone causes striking short term increases in mortality, mainly from thrombotic and respiratory disease.2 Non-thermal seasonal factors such as diet may also affect mortality.3 The increases in mortality are greater in London than in regions surveyed in continental Europe.4 We used multiple regression to assess the proportion of excess winter mortality that was attributable to influenza in south east England.