BACKGROUND: Intramedullary screw fixation of the proximal ulna can be used for fixation of the ulnar component in total elbow arthroplasty. Our purpose was to use computed tomography (CT) to characterize proximal ulna anatomy with respect to intramedullary screw fixation, and then to validate this templating process by inserting intramedullary screws into 3-dimensional (3D)-printed models. METHODS: Thirty elbow CT scans were reformatted in the axis of the proximal ulna. Screw placement was templated by fixing a length at 78 mm distal to the centerline of ulnohumeral rotation and measuring diameter, and then fixing the screw pitch diameter to 5.5 mm and measuring length. Three-dimensional models were printed for 5 patients, and intramedullary screws were advanced as distal as possible until endosteal fit was achieved. RESULTS: All patients had an anatomic limit for intramedullary screw fixation, due to dorsal angulation, varus angulation, or both. At 78 mm distal to the centerline of rotation, mean screw diameter was 5.4 mm (range, 3.2-8.0). When fixing screw diameter to 5.5 mm, the mean screw length was 79.9 mm (range, 64.2-107.9). All intramedullary screws were placed in the 3D models within 3 mm of the templated length, with correlation coefficient 0.992. CONCLUSION: This study characterized proximal ulna anatomy in the context of intramedullary screw fixation. Templating allows surgeons to predict intramedullary screw sizing, and a broad range of screw lengths and diameters is required when attempting intramedullary screw fixation for placement of the ulnar component in uncemented total elbow arthroplasty.