We assessed the hourly occupancy of our intensive care unit by high dependency patients over an 8-week period using the criteria established by the Working Group on Guidelines on Admission to and Discharge from Intensive Care and High Dependency Units published by the National Health Service Executive. High dependency patients accounted for 1914 bed hours (21.6%) out of a potential available total of 8880 hours. Measurement of Therapeutic Intervention Scoring System points and Acute Physiology and Chronic Health Evaluation II scores confirmed that categorising patients according to the new guidelines produced significantly different populations of patients. Mean (standard deviation) Therapeutic Intervention Scoring System points for intensive care status patients were 38.57 (10.40) compared to 21.65 (5.98) points for high dependency status patients (p < 0.001). Median (range) Acute Physiology and Chronic Health Evaluation II score for intensive care status patients was 16 (1-45) compared to 11 (1-27) for high dependency status patients (p < 0.0001). Calculating bed occupancy with different definitions for the whole of our intensive care unit population during the 8 weeks revealed a range of occupancies between 85.3% and 107.3%. We recommend the intensive care unit bed occupancy should be calculated in a standard manner nationally to allow comparison between units. We suggest that hourly occupancy be adopted as the universal method.