The objectives of this study were to identify factors associated with decisions concerning triage and admission to the intensive care unit and to describe the outcome of patients referred to intensive care unit for admission. The study was a single-centre, prospective, observational study. It was performed in the general intensive care unit of a tertiary regional hospital, over the period of February to June 2009. The patients were non-elective, acute medical in-patients. For 100 patients referred, only 36 were admitted to the intensive care unit. The remaining 64 were declined admission: nine were declined admission because they were assessed as too sick to benefit, 41 were declined admission because they were assessed as too well to benefit and 14 were deemed to potentially benefit from intensive care unit admission but were not admitted ('triage'). Patients most likely to receive triage decisions were medical in-patients who had expressed wishes about end-of-life care, who were functionally limited with co-morbid conditions affecting their performance status. Patients referred by Resident Medical Officers were also more likely to receive a triage decision. Age, gender Aboriginal and Torres Strait Islander status, diagnostic category and reason for referral did not impact on admission or triage decisions. Bed status in intensive care unit at the time of referral affected neither admission nor triage decisions. Hospital mortality in patients deemed too well to benefit from intensive care unit was 7.3%, suggesting that all patients referred for consideration of admission to intensive care unit should be classified as 'high risk'.