The aim of this paper is to analyse critically the use of age as a criterion to ration scarce life-sustaining resources within the intensive care environment. Insufficient funding to meet the escalating costs of health care has resulted in a scarcity of life-sustaining resources. Although an explicit policy of rationing by age within the United Kingdom (UK) has not been formulated, decisions to withhold or withdraw treatment are already being made on the basis of patients' biological age rather than medical need. Three contrasting arguments are analysed: the 'equal worth', 'fair innings' and 'prudential lifespan' arguments. In certain circumstances rationing by age is both morally permissible and justified. However, the capacity to benefit from treatment has to be considered whatever the age of the individual and any measure of benefit needs to take a broad range of medical, ethical and economic factors into account. If age is to be used, as a criterion to ration limited resources explicit, national guidelines need to be developed and applied consistently to ensure that arbitrary differences in the treatment older people receive does not occur.