A 26-year-old female, the elder of monozygotic twins, presented with slow progressive numbness and pain in her left arm. Magnetic resonance (MR) imaging showed syringomyelia with Chiari malformation. The patient’s birth had been difficult with prolonged delivery time, breech delivery, and neonatal asphyxia. MR imaging of the patient’s twin sister showed mild tonsillar ectopia, but absence of syringomyelia. This younger sister was born without problems. The patient underwent syringosubarachnoid shunt at the C5-6 level. The syrinx was collapsed promptly, and her symptoms disappeared. This case of syringomyelia with Chiari malformation in one of twins suggests that birth injury is likely to be a cause of the pathogenesis of syringomyelia.