Detection of a posterior glenoid labral lesion can be challenging. Clinicians may overlook this diagnosis because of its vague symptoms, unlike rotator cuff tear or adhesive capsulitis. Together with magnetic resonance (MR) imaging, shoulder MR arthrography is considered the imaging method of choice for the detection of posterior glenoid labral lesions. However, MR arthrography is associated with high cost and low accessibility, and to circumvent these shortcomings, efforts are being made to use sonography (US). However, prior experience in shoulder US is required to evaluate glenoid labrum using US because glenoid labrum is not located superficially and is surrounded by the rotator cuff musculature. There were a few studies that reported the potential for arthrosonography in finding the tear of anterior glenoid labrum and rotator cuff. Until now, however, there was no report regarding arthrosonography in posterosuperior glenoid labral tear and its efficacy and potential for overcoming the limitations of conventional US. In this report, we described 3 cases with posterosuperior glenoid labral tear that were not diagnosed by conventional US but by arthrosonography. In addition, the authors also present their history, physical examinations, and response to treatment, which may be helpful in the diagnosis of posterosuperior glenoid labral tear.