Herpes zoster, commonly known as shingles, is an infectious viral disease characterized by painful, unilateral skin blisters occurring in specific sensory dermatomes. Motor paresis is reported in 0.5% to 5% of patients. Although the mechanism of zoster paresis is still unclear, the virus can spread from the dorsal root ganglia to the anterior horn cell or anterior spinal nerve roots. It rarely involves the brachial plexus. We report a case of brachial plexitis following herpes zoster infection in which pathological lesions were diagnosed using brachial plexus magnetic resonance imaging and treated with ultrasound-guided perineural corticosteroid injection.