As more research is undertaken on the elderly, accurately assessing changes in their quality of life becomes increasingly important. Generic instruments are the most popular method to assess quality of life, and one of the most widely used is the EQ-5D. However, the range of dimensions, sensitivity of scales and completion rates have been raised as concerns when using this measure with the elderly. The AQoL is a newer instrument which offers greater richness in dimensions of health covered, and potentially offers greater sensitivity to changes in quality of life. This paper presents the results of a 'head-to-head' comparison of the EQ-5D and AQoL in terms of practicality, construct validity, agreement (of absolute scores and their change over time) and sensitivity to change, as part of a randomised controlled trial in the elderly. Poor agreement was found between both the absolute scores from each instrument and change in scores over time. Although the AQoL appeared to have more favourable construct validity, the EQ-5D was easier to administer, had a higher completion rate, and appeared more sensitive to change. We conclude that the AQoL is probably less well suited to measuring health status in a very elderly population than the EQ-5D.