Traumatic peripheral nerve injury can lead to significant long-term disability for previously healthy persons. Damaged nerve trunks have been traditionally repaired using cable grafts, but nerve transfer or neurotization procedures have become increasingly popular because the axonal regrowth distances are much shorter. These techniques sacrifice the existing nerve pathway, so muscle reinnervation depends entirely on the success of the repair. Providing a supplemental source of axons from an adjacent intact nerve by using side-to-side anastomosis might reinnervate the target muscle without compromising the function of the donor nerve. The authors report a case of biceps muscle reinnervation after side-to-side anastomosis of an intact median nerve to a damaged musculocutaneous nerve. The patient was a 34-year-old man who had sustained traumatic injury primarily to the right upper and middle trunks of the brachial plexus. At 9 months after the injury, because of persistent weakness, the severely damaged upper trunk of the brachial plexus was repaired with an end-to-end graft. When 8 months later biceps function had not recovered, the patient underwent side-to-side anastomosis of the intact median nerve to the adjacent distal musculocutaneous nerve via epineural windows. By 9 months after the second surgery, biceps muscle function had returned clinically and electrodiagnostically. Postoperative electromyographic and nerve conduction studies confirmed that the biceps muscle was being reinnervated partly by donor axons from the healthy median nerve and partly by the recovering musculocutaneous nerve. This case demonstrates that side-to-side anastomosis of an intact median to an injured musculocutaneous nerve can provide dual reinnervation of the biceps muscle while minimizing injury to both donor and recipient nerves.