This study aimed to determine the accuracy and reliability of visual estimation of limb alignment and knee flexion by orthopaedic surgeons when compared to recordings done by computed navigation. Orthopaedic surgeons attending a national conference were asked to place a lower limb synthetic bone model in 6 positions of the knee in the coronal and sagittal planes. These were simultaneously quantified and recorded by a computer navigation system. In the sagittal plane, 44%, 54% and 60% of the surgeons deviated by more than 5 degrees when positioning the knee in 0 degrees flexion, 10 degrees flexion and 90 degrees flexion respectively. In the coronal plane, 15%, 12% and 8% of the surgeons deviated by more than 5 degrees when positioning the knee in 0 degrees varus/valgus, 5 degrees varus and 5 degrees valgus respectively. Only 25% of the surgeons could position the knee both within 3 degrees of neutral varus/valgus and within 5 degrees of neutral flexion. Accuracy of visual estimation was not different when surgeons were compared based on time since residency, experience with TKA and experience with computer-assisted TKA. Visual estimation of knee alignment in both the sagittal and coronal plane is prone to error and may lead to inaccurate limb alignment during procedures such as TKA.