Background: Early diagnosis of traumatic acute full-thickness rotator cuff tears (FTRCT) is important to offer early surgical repair. Late repairs following fatty infiltration of the rotator cuff muscles have less favorable results. We think that physical therapists are valuable diagnosticians in a screening process. The objective of this study was to evaluate the usefulness of physical therapists as first-line diagnosticians in detecting acute traumatic FTRCT. Methods: Between November 2010 and January 2014, 394 consecutive patients having an age between 18 and 75 years who sought medical care because of acute shoulder trauma with acute onset of pain, limited abduction and negative plain radiographs were included in the study. A clinical assessment was conducted by a physical therapist 1 week after the trauma. The patients were divided into three groups by the physical therapist according to the findings: FTRCT (Group I, n = 122); sprain (Group II, n = 62); or other specific diagnoses (Group III, n = 210). Group III patients were discharged and excluded from the study. Magnetic Resonance Imaging shoulder was performed for all Group I patients and for all patients with persistent symptoms in Group II. Results: 79/184 patients had FTRCTs documented by MRI in groups I and II. The clinical assessment of the physical therapist had a sensitivity of 85%, specificity of 68%, and usefulness index of 0.45 (> 0.35 considered useful) for diagnosing FTRCT. Conclusion: Physical therapists can be useful as first-line diagnosticians in detecting traumatic FTRCT.