Segmental zoster paresis, a rare complication of herpes zoster, is characterized by focal, asymmetric motor weakness in the myotome that corresponds to the dermatome of the rash. The pathogenesis of segmental zoster paresis is inflammation caused by the spread of the herpes virus. Motor damage may affect the root, plexus, or peripheral nerve. A woman in her early seventies with right shoulder pain and shoulder girdle muscle weakness was diagnosed with involvement of the C5-7 motor roots and upper truncus of the brachial plexus as a complication of herpes zoster. Recognition of herpes zoster as a cause of acute motor weakness is important in avoiding unnecessary interventions as well as in determining the treatment and outcome of the patient. This case is presented to emphasize that herpes zoster infection may be complicated by segmental paresis, which should be considered in the differential diagnosis of acute painful motor weakness of the upper extremity.