Isolated teres minor denervation is an uncommon finding on sonographic examination. We present a case of a 64-year-old man with increased echogenity of the teres minor muscle and a slight reduction in muscle bulk. Investigation of a suspected axillary nerve lesion included a detailed sonographic examination of the posterior shoulder and the axillary space, followed by MR imaging and electrophysiologic testing. This case demonstrates the potential importance of examining rotator cuff muscles when performing sonographic examination of the shoulder in patients with persistent symptoms, no history of trauma, and absence of tendon tears.