Anatomical studies of the deltoid muscle were performed on 16 cadaver shoulders. The anatomy of the axillary nerve, the vascular pedicles, and the musculocutaneous perforators was assessed. These studies confirmed that part of the deltoid muscle can be used as a vascularised flap to cover defects of the shoulder while leaving some viable functioning muscle intact. We report the use of hemideltoid flaps to treat chronic radionecrotic ulcers involving the shoulders of two patients. In the first, the posterior part of the muscle was used as a local muscle flap. In the second, the anterior part of the muscle was raised with overlying skin to form a musculocutaneous flap. The flaps remained healed at one year follow-up. These soft tissue radionecrotic defects over the shoulder are an uncommon late complication of radiotherapy for breast cancer. Pedicled or free flaps are now recognised as the preferred methods of treatment.