We report the case of an 86-year-old man with acute left shoulder pain, followed by left limb monoparesis and a herpetic rash on the left upper limb and thoracic region. This situation presented a diagnostic challenge because of the simultaneity of symptoms attributable to Parsonage-Turner syndrome and herpes zoster neuropathy. A detailed clinical history, physical examination and electroneuromyography were essential to distinguish the neurological structures involved and to ascertain the diagnosis.