Ireland shares with other developed countries the prospect of rapid and sustained population ageing. The age distribution of the Irish population is undergoing a dramatic change at present and this trend is predicted to continue into the future. 1 People are living longer, and older persons represent a larger proportion of the population. In Ireland, the proportion of the population aged 565 years has remained steady at $11% for the past 40 years. However, it is projected that this proportion will rise to 14% by 2021 and to 19% by 2031. 2 The greatest increase will be in the oldest old, aged 480 years, which is expected to more than treble by 2036. 2 This change in the demographic profile of the Irish population poses a major public health challenge.

Unlike the situation in the USA, 3, 4 the UK 5 and many other developed countries, 6, 7 there have been no large population-based cohort studies in Ireland to inform research on healthy ageing. Whereas a number of studies have provided population-based data on the health status of older people living in Ireland, 8–10 many questions remain unanswered. The Irish Longitudinal Study on Ageing (TILDA) is a large prospective cohort study of ageing, which includes an assessment of the social, economic and health circumstances of community-resident older people living in Ireland. The study has been harmonized with leading international research so as to ensure adoption of best practice and comparability of results. The Irish government, The Atlantic Philanthropies and Irish Life plc have provided funding for the study. Ethical approval has been obtained from the Trinity College Dublin Research Ethics Committee.