We describe 3 patients who developed injury of upper and middle brachial plexus trunks during robotic-assisted prostatectomy, and review factors potentially associated with this type of injury. Three patients underwent robotic-assisted prostatectomy. Surgical exposure was facilitated by steep head-down tilt position. To secure patients and prevent sliding on the operating table, shoulders were supported with moldable beanbags. In all 3 cases, the left arm was abducted to approximately 90°, and the right arm was adducted. Postoperatively, all patients were diagnosed with left arm upper and middle trunk brachial plexopathies. The combination of arm abduction, extreme head-down position, and shoulder immobilization with beanbags resulted in several mechanistic forces that may have contributed to the development of brachial plexopathy in our patients. Steep head-down tilt may result in cephalad slide of the torso in relation to an abducted arm. When shoulder restraints are used to secure the patient, the compensatory movement of the shoulder girdle of an abducted arm is impeded. This may result in injurious stretching and compression of the brachial plexus, especially the upper and middle trunks. When steep head-down position is needed to facilitate surgical exposure, clinicians should consider adduction and tucking of both arms, and use of other methods to prevent sliding on the operating room table that do not require the use of restraints across the shoulder girdle.