Purpose: Obesity is associated with worse trauma outcomes and has been proposed as a modifier in trauma triage. Early identification, however, commonly relies on visual assessment. This study evaluates the accuracy of visual obesity classification and height and weight estimation by trauma care providers at first patient contact. Methods: This prospective observational study was conducted at a Level I trauma centre. Paramedics, emergency department (ED) nurses, and ED physicians independently estimated patient height, weight, and obesity status on arrival. Measured anthropometric values served as the reference standard. Diagnostic performance metrics for obesity classification and estimation error metrics for height and weight were calculated. Results: One hundred and forty-three trauma patients were included (68.5% male; median age 44 years), with an obesity prevalence of 28.7%. Overall sensitivity for visual obesity classification was 80.2% and specificity was 89.8%, with no significant differences between professional groups. Height estimation was more accurate than weight estimation, but substantial inter-individual variability was observed for both parameters. Internal consistency between visual obesity classification and BMI derived from estimated height and weight was high (87.6%). Conclusion: Visual assessment of obesity in trauma patients demonstrates high specificity but only moderate sensitivity, resulting in a clinically relevant proportion of patients with obesity being missed. Given the variability of anthropometric estimation and the importance of early risk stratification, visual assessment alone appears insufficient for use as an independent trauma triage criterion, supporting the need for more objective methods of early obesity identification.