Background: Initial clinical evaluation (ICE) is traditionally considered a useful screening tool to identify frail patients during the pre-operative assessment. However, emerging evidence supports the more objective assessment of cardiorespiratory fitness (CRF) via cardiopulmonary exercise testing (CPET) to improve surgical risk stratification. Herein, we compared both subjective and objective assessment approaches to highlight the interpretive idiosyncrasies. Methods: As part of routine pre-operative patient contact, patients scheduled for major surgery were prospectively ‘eyeballed’ (ICE) by two experienced clinicians prior to more detailed history taking that also included American Society of Anaesthesiologists score classification. Each patient was subjectively judged to be either ‘frail’ or ‘not frail’ by ICE and ‘fit’ or ‘unfit’ from thorough review of the medical notes. Subjective data were compared against the more objective validated assessment of post-operative outcomes using established CPET ‘cut-off’ metrics incorporating peak pulmonary oxygen uptake ( V̇O 2PEAK), V̇O 2 at the anaerobic threshold ( V̇O 2-AT) and ventilatory equivalent for carbon dioxide that collectively informed risk stratification. These data were retrospectively extracted from a single-centre prospective National Health Service database. Data were analysed using the Chi-square automatic interaction detection decision tree method. Results: A total of 127 patients examined that comprised 58 % male and 42 % female patients aged 69 ± 10 y with a BMI of 29 ± 7 kg/m 2. Patients were poorly conditioned with a peak pulmonary oxygen uptake almost 20 % lower than that predicted for age, sex-matched healthy controls with 35 % exhibiting a V̇O 2-AT <11 mL/kg/min. Disagreement existed between the subjective assessments of risk with ~34 % of patients classified not frail on ICE were considered unfit by notes review ( P < 0.0001). Furthermore, ~35 % of patients considered not frail on ICE and ~31 % of patients considered fit by notes review exhibited a V̇O 2-AT <11 mL/kg/min and of these, ~28 % and ~19 % were classified as intermediate-to-high risk. Conclusions: These findings highlight the interpretive limitations associated with the subjective assessment of patient frailty with surgical risk classification underestimated in up to a third of patients compared to the validated assessment of CRF. They reinforce the benefits of a more objective and integrated approach offered by CPET that may help improve perioperative risk assessment and better direct critical care provision in patients scheduled for ‘high-stakes’ surgery including open TAAA repair.