The multiple regression statistical method has already been used to estimate excess deaths attributable to influenza in England and Wales by winter period. Now we report further studies of deaths by age group and certified cause of death. During the ten winters since the influenza A/Hong Kong (H3N2) virus first arrived (1968/69 to 1977/78) there have been about 120,000 excess deaths. Of these about 82% were estimated to be in those aged 65+ years, 17% in the 40-64 year age group and 1% in younger adults. Sixty-seven per cent were certified as due to respiratory disease and 31% due to circulatory system disease. Respiratory deaths increased in all age groups during an epidemic, but of the deaths certified as due to circulatory disease, cerebrovascular deaths were mostly in the 65+ age group and ischaemic heart disease deaths in the 40-64 year age group. In this 40-64 year age group there was evidence that the effects of cold weather and epidemic influenza were multiplicative rather than additive. During the worst influenza winter of 1969/70 respiratory deaths increased by approximately 55% and circulatory system deaths by 4%. Deaths in the elderly increased by 10%, in those aged 40-60 years by 8% and in younger adults by 4%. There was no evidence that excess deaths are followed by a deficit during the following year.