The United Kingdom Medical Research Council and Economic and Social Research Council have funded, since 1982, a longitudinal study of cognitive change in old age carried out on over 6000 volunteers aged between 50 and 96 years and resident in Newcastle-upon-Tyne and Greater Manchester. The Medical Research Council has guaranteed further funding until 1977. This paper describes the history of the study, the test batteries employed, the demographics of populations tested and the amount, and selectivity, of attrition by death and withdrawal from the study. Further aims of the study, and parallel work carried out on a number of related projects concerned with the epidemiology, time-course and everyday impacts of cognitive changes in normal old age are also discussed.