Demand for intensive care is growing. There are no contemporaneous consensus guidelines on which patients should be referred to intensive care. Prognostic scoring systems predict survival, but are of limited use for individual patients. Some groups of patients have historically been regarded as having a very high mortality after admission to intensive care, raising questions about the appropriateness of advanced organ support in these patients. We reviewed the existing literature on outcomes of patients admitted to intensive care with chronic obstructive pulmonary disease, liver cirrhosis and haematological malignancies. We identified specific markers indicating a poor prognosis in each group, and also identified common risk factors predicting a high mortality across all groups. Multiple organ failure at the time of referral to intensive care predicts a very poor outcome. Physical factors indicating a limited functional capacity also predict high mortality, suggesting that frailty has a significant impact on intensive care outcome. It is not medically appropriate to devote limited ICU resources to patients without reasonable prospect of significant recovery when patients who need those services, and who have a significant prospect of recovery from acutely life-threatening disease or injury are being turned away due to lack of capacity