Brachial plexuses of an adult female capuchin monkey (Cebus capucinus) were observed macroscopically. The main characteristic features of the organization of the plexus were as follows: Substantially the same organization was observed in the plexuses on both sides. The plexuses were formed by the union of the 5th–8th cervical nerves and the 1st thoracic nerve. The component from C5 contributed only to the superior posterior division; consequently the superior trunk in the strict sense was lacking. The medial cord was a peripheral extension of the inferior anterior division and formed a “common trunk” with the lateral root of the median nerve. Therefore, the medial root of the median nerve in the strict sense was absent, and the median nerve arose from the “common trunk” with the ulnar nerve. In the plexus on the right side, a long aberrant branch was found, which arose as an “extra” anterior divison of the middle trunk and joined peripherally the medial cord at a point where the cord formed the “common trunk” with the lateral root of the median nerve. These findings were compared with previous data obtained from other primates.