Reinnervation of the axillary nerve (AXN) by intraplexal nerve donors yields satisfying results in the treatment of patients with upper and upper-extended brachial plexus (BP) palsy. In cases of complete BP palsy with no viable BP elements, the use of extraplexal donors is necessary, such as spinal accessory nerve (SAN) and phrenic or intercostal nerves. Poor outcomes following intercostobrachial anastomosis were the reason for the introduction of SAN as a donor, especially in complete BP palsy following root avulsion. This chapter aims to present the authors’ experience concerning AXN reinnervation using SAN as a donor, complemented by the results of the literature review. The general considerations, surgical procedure, and outcomes are discussed, as well as the advantages and disadvantages of this technique.