Cubital tunnel syndrome is the second most common compressive neuropathy of the upper limb after carpal tunnel syndrome and results from entrapment of the ulnar nerve around the elbow. High-resolution ultrasound has become a central diagnostic modality because of its excellent spatial resolution, capacity for dynamic assessment, and broad availability in clinical practice. This review offers an integrated and updated overview of the ultrasonographic evaluation of the ulnar nerve in cubital tunnel syndrome, detailing relevant anatomy, characteristic normal and pathological appearances, and key considerations in postoperative follow-up. The ulnar nerve may be compressed at several anatomical sites, including the arcade of Struthers, the retrocondylar groove, Osborne’s ligament within the cubital tunnel, and the aponeurosis between the two heads of the flexor carpi ulnaris. Typical sonographic abnormalities include focal or segmental nerve enlargement, disruption or loss of the normal fascicular architecture, and changes in echogenicity. Dynamic maneuvers during ultrasound examination can further identify nerve subluxation, dislocation, or snapping over the medial epicondyle, all of which may contribute to clinical symptoms. Postoperative ultrasound evaluation is increasingly important for detecting complications or persistent compression following in-situ decompression, medial epicondylectomy, or anterior transposition. A standardized and reproducible ultrasound protocol is therefore essential for accurate diagnosis, appropriate management, and follow-up. Radiologists play a pivotal role in this multidisciplinary approach by providing detailed imaging assessments that guide surgical decision-making and help optimize patient outcomes.