This report introduces a technique for treating >5 cm of bone loss from the distal part of the ulna due to tumor resection or trauma. The distal part of the forearm is stabilized by an advancement lengthening osteotomy of the ulna in combination with a ligamentoplasty with a portion of the flexor carpi ulnaris tendon. We present the cases of two patients in whom this technique was used to treat giant-cell tumor of the distal part of the ulna. The patients were informed that data concerning their cases would be submitted for publication, and they consented. Two patients, an eighteen-year-old man (Case 1) and a forty-eight-year-old woman (Case 2), were referred to our institution with a symptomatic mass in the distal part of the right forearm. Radiographs, magnetic resonance imaging (MRI), and computed tomography (CT) scans suggested the diagnosis of giant-cell tumor (Fig. 1). This diagnosis was confirmed by a surgical biopsy and histopathological study in each patient. Neither patient had evidence of metastatic giant-cell tumor. Fig. 1 Case 2. Anteroposterior radiograph (image on left) of the distal part of the forearm shows the level of the proximal resection osteotomy (red line). Axial CT (lower right) and coronal MRI (upper right) views of the giant-cell tumor show a Campanacci grade-3 tumor with cortical breakthrough. The surgical technique used to treat these lesions was essentially the same for both patients. We performed an en bloc resection of the tumor, with the resection margin 3 cm proximal to the tumor as seen on the preoperative MRI. The gap after resection was 8 cm in one patient and 6 cm in the other patient. We performed longitudinal ulnar osteotomies of 8 cm and 6 cm, for lengthening of 6 cm and 4 cm, respectively, because a minimum overlapping length of 2 cm is needed for …