Extensive soft tissue defects of the upper extremities were reconstructed with major fillet flaps in nine patients over a 5-year period at two institutions. Etiologies included trauma and tumor resection. Defect locations were the shoulder ( n=3), combined defects of the shoulder plus neck, arm or chest wall ( n=4) as well as one upper arm and one forearm defect. Seven of nine flaps required microsurgical free tissue transfer. Fillet flaps harvested from amputated parts represent the "spare part" concept, providing coverage of defects without additional donor site morbidity. Unlike the classic "spare part" fillet flap concept, the partial or complete conversion of an anatomically intact arm was performed for the coverage of large defects, especially for tumor reconstruction, in this series. Fillets flaps facilitate reconstruction in difficult and complex cases. Major fillet flaps represent a valuable option for reconstruction in the upper extremities with either pedicled or free tissue transfers involving extensive tissue defects.