The purpose of our study was to correlate radiographic characteristics with rotator cuff tendon injury on magnetic resonance imaging after fractures of the proximal humerus. We prospectively obtained magnetic resonance imaging on 30 patients with proximal humerus fractures after classifying each fracture radiographically using Neer and AO systems and determining the displacement of the greater tuberosity. Twelve patients (40.0%) had either complete ruptures or avulsions of at least one of the rotator cuff muscles. No abnormality was identified in the rotator cuff musculature in nine patients (29%). Severity of injury to the rotator cuff tendons increased substantially with respect to increasing AO and Neer classes and 5 mm or greater displacement of the greater tuberosity fragment. Additional study is needed to determine the exact role of rotator cuff tendon injury in the ultimate function attained by patients with proximal humerus fractures.