These new ageing studies, which share a comparable template, provide rich sources of information for researchers interested in the dynamics of health, socioeconomic status, retirement, and wellbeing among ageing populations. Their panel nature allows us to investigate the nature and determinants of within-person and within-household experiences in retirement and health onsets, and the manner in which these central life domains co-relate. There are now more than 25 countries in the world who have initiated such comparable longitudinal ageing studies and more countries are certainly on the way.An important concern with all panel studies, and particularly those focused on an older population, is the potential for bias caused by individuals non-randomly dropping out of the survey over time. If attrition from a survey is systematically related to outcomes of interest or to variables correlated with these outcomes, then not only will the survey cease to be representative of the population of interest, but estimates of the relationships between different key outcomes, especially in a longitudinal context, may also be biased.The issue of non-response in longitudinal surveys-both initial non-response and subsequent attrition-has a distinguished history in survey research and statistics (Sudman and Bradburn, 1974, Groves and Couper, 1998, Little and Rubin, 1987. Most of the existing literature has focused on non-ageing panels in the United States, especially during earlier time periods when attrition rates typically were considerably lower (Becketti et al., 1988;Fitzgerald et al., 1998;Lillard and Panis, 1998; Zapel, 1998).In this paper we present results of an investigation into observable characteristics associated with attrition in ELSA and the HRS, with a particular focus on whether attrition is systematically related to health outcomes and socioeconomic status (SES) links between health and SES is one of the primary goals of the ELSA and HRS, so attrition correlated with these outcomes is a critical concern.We begin by looking at raw rates of attrition in the two surveys, and show that panel attrition is a far greater problem in ELSA than in HRS. We consider several possible explanations for ELSA's poorer retention rates, including the greater 'maturity' of HRS (which has been running for ten years longer than ELSA), differences in sampling rules and procedures used in the two surveys, the 'quality' of the two respective survey organizations, and differences in incentives offered to respondents. We conclude that none of these explanations alone or together seems sufficient to account for the disparity in attrition rates between the two surveys.Having documented raw attrition rates in ELSA and HRS, we then consider the possible bias such attrition could introduce into estimates of disease prevalence derived from the two surveys. In recent papers, we have used data from these surveys to demonstrate that middleaged and older Americans are substantially less healthy than their English counterparts, across a range of impo...