Reconstruction after radical forequarter amputation for recurrent proximal extremity sarcoma is challenging because the defect is significant, and the axillary or subclavian vessels are resected with the tumor, indicating that the pedicle of nearby flaps is often cut off. Free flaps are commonly used to cover the defect, but the donor site morbidity is problematic. Another problem with resecting the axillary or subclavian vessels is difficulty obtaining recipient vessels with matching calibers for another free flap. The authors presented 2 cases that successfully solved all these problems by covering the defects by the forearm fillet flaps.The forearm fillet flap has the advantage of using a portion that is usually discarded, so there is no donor site morbidity. Moreover, using the brachial artery as the pedicle of the flap allows the anastomosis to the stump of the resected axillary or subclavian artery because differences in caliber are slight.The use of the forearm fillet flaps has been reported less frequently than the fillet flaps in the lower extremities, and most cases are posttraumatic. In cases of trauma, complications are reported to occur in about 1 in 4 patients, but in cases after tumor resection, ischemic time can be controlled, and there are no risks of contamination or unnoticed forearm damage, so more stable results can be expected as in this report.Using the free flap from the distal portion of the resected upper limb, especially in cases with a short prognosis, is a viable option that effectively minimizes damage to the donor site and maintains quality of life.