Segmental zoster paresis of the left upper limb in a pediatric patient.Segmental zoster paresis is a rare complication of herpes zoster characterized by focal, asymmetrical motor weakness in the myotome that corresponds to the dermatome of the rash. Segmental zoster paresis typically develops within 2-3 wks of cutaneous zoster and predominantly affects the middle-aged and elderly populations. Motor complications rarely develop in children and young adults, but when they do develop, involvement is usually confined to cranial and truncal muscles, with sparing of the limb musculature. A 10-yr-old boy with Fanconi's anemia developed left upper limb weakness because of involvement of C5 motor roots as a complication of herpes zoster. Recognizing motor zoster as a cause of acute motor weakness in a pediatric patient is important in avoiding unnecessary interventions and optimizing treatment.