Background <p>The American Society of Anaesthesiologists Physical Status (ASA-PS) classification system is the most widely used tool for estimating perioperative risk. Despite its widespread application, the ASA-PS is based solely on the subjective assessment of the patient’s clinical condition and comorbidities, which leads to considerable inter-rater variability. The aim of this study was to investigate interprofessional differences in ASA-PS scoring between surgeons and anaesthesiologists.</p> Methods <p>This prospective observational study involved patients who were scheduled for elective or emergency surgery. The patients were independently evaluated using the ASA-PS classification by treating anaesthesiologists and surgeons with varying levels of experience. Following data collection, an interdisciplinary board comprising senior anaesthesiologists and surgeons retrospectively assigned reference ASA-PS scores. Inter-rater agreement was analysed using Cohen’s kappa (<i>κ</i>).</p> Results <p>In total, 684 were included in the study. Surgeons assigned lower ASA-PS classes more frequently, with 16.81% of ratings corresponding to ASA-PS I and 52.05% to ASA-PS II, compared to 6.29% vs. 40.50% among anaesthesiologists. In contrast, anaesthesiologists more often classified patients as ASA-PS III (50.88%), than surgeons (28.51%). Agreement with the reference board was higher among anaesthesiologists (<i>κ</i> = 0.36) than among surgeons (<i>κ</i> = 0.21). The interprofessional agreement between surgeons and anaesthesiologists was low (<i>κ</i> = 0.25), which highlights the significant variability in clinical judgment between disciplines. ASA-PS assessments were more frequently performed by residents among surgeons than among anaesthesiologists (90.35% vs. 69.74%; <i>p</i> &lt; 0.0001).</p> Conclusion <p>The findings underscore the substantial inter-rater variability in ASA-PS scoring between surgical and anaesthesiological teams. While ASA-PS classification of ≥III remain clinically relevant and is widely used as a predictor for perioperative risk, the observed discrepancies may affect risk stratification in clinical practice. As most of ASA-PS assessments, especially in the surgeon group, were performed by residents, these results highlight the importance of structured training, and potentially supplementary objective tools to improve consistency and reliability in preoperative risk assessment.</p> Trial registration <p>The study was registered at ClinicalTrials.gov (No. NCT02995499) and the German Clinical Trial register (No. 00011311, 12/2016).</p>