Background Restoration of shoulder function is a primary goal when treating patients with traumatic brachial plexus injury. A concomitant rotator cuff tear may alter the treatment approach and prognosis for these individuals. The purpose of this study was to define the prevalence of rotator cuff tears in patients with traumatic brachial plexus injuries. Methods This is a retrospective review of 280 adult patients with traumatic brachial plexus injury treated at a single institution over a twelve-year period. An upper-extremity magnetic resonance imaging (MRI) scan was acquired for all patients as part of the initial evaluation for posttraumatic brachial plexus injury. The radiographic and clinical data on these patients were reviewed to document partial or full-thickness rotator cuff tears, mechanism and location of the brachial plexus injury, and age. Results Twenty-three patients (8.2%) had a full-thickness rotator cuff tear: one patient had tears involving three tendons, eight patients had tears involving two tendons, twelve patients had a single-tendon tear, one patient had a single-tendon tear in each shoulder, and one patient had a single-tendon tear in one shoulder and a two-tendon tear in the other. Twenty-one tears involved the supraspinatus, eight involved the infraspinatus, and seven involved the subscapularis. Thirteen patients underwent surgical repair of the rotator cuff. The average age of the patients in this cohort was 33.4 years, and older age was associated with an increased risk of full-thickness rotator cuff tears (odds ratio [OR], 1.06 per year). Patients with infraclavicular brachial plexus injury had a significantly higher rate of full-thickness rotator cuff tears. Conclusions Concomitant rotator cuff tears are present in approximately one in ten patients with traumatic brachial plexus injury. These injuries may contribute to shoulder dysfunction; therefore, evaluation of the rotator cuff with imaging studies is appropriate when formulating treatment strategies. Level of Evidence Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.