The purpose of our study was to determine the accuracy of orthopaedic patient's reported height, weight, and body mass index (BMI). We hypothesized that patient's age, sex and/or BMI may affect their accuracy. We performed a prospective, observational study in the setting of our orthopaedic clinic. Differences between self-reported and actual values were calculated. Patients were categorized based on their age (< 65 vs. ≥ 65), sex, and actual BMI (<30 vs. >30). Student t-test and chi-square test were used to compare groups. Our study included 329 patients. Patients were more likely to underestimate weight (p < 0.001) and overestimate height (p = 0.007). Comparing patients with a BMI < 30 and > 30, height overestimation (0cm vs. 1.14cm, p = 0.004) and weight underestimation (0.09kg vs. 1.29kg, p = 0.02) discrepancies were greater in the BMI > 30 group. Patients, particularly with a BMI >30 kg/m2, over-estimate their height and under-estimate their weight. (Journal of Surgical Orthopaedic Advances 30(3):176-180, 2021).