The ASA classification is an assessment of the patient’s preoperative physical status. On its own, the ASA classification of physical status is not a predictor of operative risk. Operative risk is a combination of: the physical status of the patient; the physiological derangement that the procedure will cause; the skill and experience of the operator; the skill and experience of the anaesthetist (including the choice of anaesthetic); and the physiological support service in the peri-operative period (including pre-operative optimisation and critical care). A patient for an elective procedure with an ASA grade of 3 or 4 needs a consultation with a senior anaesthetist as far before the proposed surgery as is possible. This will enable the patient’s physical condition to be optimised with better post-operative outcome and will reduce the chance of ‘on the day’ cancellation due to being medically unfit.