Primary Care Trusts (PCTs), charged with improving the health of their population, need to measure the extent to which patients actually benefit from the health care that is provided for them. One way of achieving this is to measure health status of patients over time. The study described here reports on the feasibility of administering the EQ-5D in general practitioner (GP) surgeries and identifies how the results might be used by practices and PCTs to improve the health of their populations. The study took place in an opportunistic sample of 1942 patients attending GP surgeries. One year later, patients who had provided contact details were sent another EQ-5D together with a request for additional information about their use of health care services in the intervening time period. A total of 770 patients completed this follow-up questionnaire. There were significant age effects associated with variation in self-reported health status and also associated with top-level Read diagnostic codes in some groups of patients. The results showed that EQ-5D could be used by individual GP practices to identify patients with specific health problems. This knowledge can also be used by PCTs and other primary care organisations, to better target scarce health resources.