Seasonal fluctuations in mortality are associated with age, outdoor temperature, and influenza. The relative excess winter mortality is approximately twice as high in the UK compared with the Scandinavian countries. Using data from Norway and England plus Wales, this study compares the effect of age, temperature and influenza on winter excess mortality in the two countries. Bivariate analyses showed that the excess winter mortality (December-March) in England and Wales was nearly twice as high in old as in middle-aged people, and also markedly higher than in Norway, while the association between excess winter deaths and influenza was of a similar magnitude. In the British data only, a marked and statistically significant negative relationship existed between outdoor temperature and excess winter mortality, corresponding to an increase of approximately 3,500 deaths in England and Wales (approximately 2/10,000 in the population aged 45 years and over) per 1 degree C reduction in winter temperature, after adjustment for age and influenza. Using data from 20 Western European countries, a highly significant positive correlation (R = 0.71, p < 0.001) was found between total mortality rates for the elderly (65 years and over) and relative excess winter mortality.