A 3-dimensional (3D) lower extremity alignment assessment system based on biplanar computed radiography, a camera calibration procedure, and 3D image fitting techniques was developed. The goal of this study was to examine the errors associated with applying this 3D technique to determine component alignment after total knee arthroplasty (TKA). Tibial and femoral component alignment after TKA (varus--valgus, flexion-extension, and internal--external angulations) in 4 patients was determined directly with reconstructions from computed tomography (CT) scans and indirectly with the proposed bone and component image fitting techniques. Mean differences between alignment values from the CT and image fitting techniques ranged from 0.18 degrees to 0.78 degrees, and maximum differences ranged from 0.30 degrees to 0.90 degrees. The proposed 3D method can be reliably used to assess component alignment after TKA.