Background: Nerve identification and safe dissection are facilitated by knowledge of nerve anatomy. New neuroanatomical insights provide understanding of anomalous innervation and discovery of redundant motor innervation may identify potential motor axon donors for nerve transfers. Knowing the distances along a nerve from a reference point to the end organ allows estimation of recovery time after nerve repair. Methods: The ulnar nerve was dissected under 3.5x magnification in 25 fresh cadaveric arms from the mid-brachium to the wrist. Using the medial humeral epicondyle (MHE) as a reference (0.0mm point), distances were measured along the nerve to branch points (with "-" connoting "proximal" to the MHE) and along the branches to their targets. Branch patterns were recorded. Means and ranges of branch intervals and lengths were calculated. Results: 1-3 elbow joint branches were found in 48% of arms with an average branch point of -16.8mm. The most proximal motor branch point was to the FCU at -2.6mm. Average branch points to the FCU humeral and ulnar heads and the common belly were 19.1mm, 22.3mm and 41.5mm respectively. Mean branch lengths to the humeral, ulnar and common bellies averaged 18.6mm, 23.2mm and 53.2mm, respectively. The humeral head had branches in 88% of arms with 0-2 branches per specimen, 100% of the ulnar heads had 1-3 branches and the common belly had 1 branch in 2/25 specimens. The FCU was the most richly innervated muscle having a mean of 2.4 branches (range 2-4). The FDS received ulnar efferents in 3/25 specimens with a mean branch point of 36.5mm and length of 32.2mm. The FDP was ulnar innervated in 96% of arms with the most proximal and mean branch points being 11.7mm and 42.0mm, respectively and mean branch length being 24.1mm. A Martin-Gruber connection from the ulnar to the median nerve was found in 6/25 specimens with a mean branch point of 72.4mm. 21/25 specimens had branches to the ulnar artery. The superficial ulnar nerve sensory branch was present in all specimens branching at an average of 186.4mm. Conclusions: The most proximal branch was not always articular. Average muscle innervation order from proximal was FCU, FDS (when present) and FDP. Occasionally the FDP was not motored by and sometimes the FDS was partially innervated by the ulnar nerve. The FDS and FCU may have motor axons that can be spared for nerve transfer.