The purpose of this paper was to study the relationship of post-menopausal hormone therapy to cardiovascular mortality by time trend analysis. Mortality and incidence figures by age and sex in 1970–1993 in Finland were obtained from published and unpublished statistics and the extent of hormone therapy use by age from previous nationwide surveys. Percent changes in mortality were calculated for different age groups and time periods (1970–1976, 1977–1987 and 1988–1993, chosen by the extent of hormone use). A theoretical reduction in mortality among 50–54 and 55–59 year old women was calculated by using the time trends among men and older women (60–64 years) as the bases and by multiplying the proportion of users by four hypothetical estimates (100, 50, 30, and 0% of benefit among users). The actual reduction in ischaemic heart disease and total cardiovascular mortality in the age groups with highest post-menopausal hormone use was not larger than in other female age groups or among men. Until 1987, the actual mortality of 50–54 and 55–59 year old women was lower than that predicted from both the data of older women and men and from the assumed benefits of hormone therapy. In the last time period the actual mortality was relatively nearer the predicted mortality both among 50–54 and 55–59 year old women. This time trend analysis does not support the claim that post-menopausal hormone therapy notably prevents cardiovascular mortality.