Objectives. To compare patient self-report of knee flexion, extension, range of motion (ROM) and American Knee Society (AKS) Pain, Knee and Functional scores with a clinician assessment. Methods. A total of 239 consecutive total knee arthroplasty (TKA) patients (290 knees) were mailed surveys with an AKS questionnaire and lateral knee photographs that showed knee ROM in 10° increments to compare their operated knee(s) ROM. Patients were subsequently seen in clinic and their ROM, AKS Pain, Knee and Functional scores were measured. Patient- and physician-reported measures were compared using independent sample t-test and correlated using Spearman's correlation coefficient. A priori rules for comparisons were based on previously published reports. Results. A total of 286 knees had both survey and clinic data available and constituted the analytic set. Patient-reported and physician-assessed extension, flexion and ROM were: 3 ± 4.8° vs 1.4 ± 4.3° (P < 0.001), 111.4 ± 14.6° vs 110 ± 12.8° (P < 0.04) and 108.6 ± 16.8 vs 108.6 ± 14.3° (P < 0.98). There was a moderate correlation between patient and physician assessments (extension = 0.31; flexion ± 0.44; ROM = 0.42; P ≤ 0.001 for all). Patient-reported and physician-assessed AKS Pain, Knee and Functional scores were: 35.8 ± 15.6 vs 43.9 ±11.1 (P ≤ 0.001), 79.8 ± 20 vs 88.9 ± 13.3 (P < 0.001) and 57.7 ± 23.1 vs 65.7 ± 26.4 (P < 0.001), respectively. Patient- and physician-assessed AKS Pain, Knee and Functional scores had moderate-high correlation (r = 0.49, 0.49 and 0.70; P ≤ 0.001 for all). Conclusion. Long-term surveillance of TKA patients may be possible using a self-report AKS, but the average 8- to 10-point difference between patient- and physician-reported AKS scores (patients reporting poorer scores) represents a substantial impact on this outcome instrument. Since patient-reported responses have clear value in global assessment, further evaluation with other validated outcome instruments is warranted. © The Author 2008. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved.