We aimed to assess the rate and type of postoperative motor deficits that might be encountered following elbow flexion reanimation using ulnar- and/or median-based side-to-end nerve transfers in patients with brachial plexus injuries. All patients who underwent elbow flexion reanimation between November 2015 and October 2017 at our facility by nerve transfer based on partial harvests of the median and/or ulnar nerves were included. Postoperative clinical assessment was conducted the day after surgery to identify motor deficits in the territory of the harvested nerves. If a clinically noticeable deficit was present, the type and extent of the deficit were noted, and postoperative clinical evaluations were conducted monthly to determine its progression. After reviewing the charts of 27 consecutive patients, 4 patients were found to have a postoperative motor deficit (15%). In all four cases, the deficit was limited to the anterior interosseous nerve (AIN) territory in patients who underwent a double transfer (i.e., ulnar-to-biceps and median-to-brachialis). With clinical impairments of the flexor pollicis longus and/or the flexor digitorum profundus of the index and third fingers initially ranging from grade-0 to grade-3 strength, full recovery to preoperative strength levels occurred in all cases after a mean of 7 months’ follow-up. Transient motor deficits may be observed in the AIN territory following elbow flexion reanimation when a median-to-brachialis nerve transfer is associated with the original Oberlin procedure.