A 5-day-old newborn girl presented with cutaneous signs of hypertrichosis, skin dimple, and subcutaneous lipoma in the lumbar region. Magnetic resonance (MR) imaging of the thoracolumbar spine demonstrated spinal dermal sinus, type H split cord malformation, and tethered cord. A small terminal syringeal cavity was also present. Five months after the diagnosis, weakness in dorsal flexion of the bilateral feet and toes was detected. Surgery to untether the cord was performed. Her deficits resolved completely. Nearly 4 years later, she was admitted with weakness in dorsal flexion of the right foot and toe. MR imaging of the spine showed holocord syringomyelia, postoperative changes, and tethered cord. No Chiari malformation was seen. Syringosubarachnoid shunt placement was performed. Terminal syringomyelia is common in cases of occult spinal dysraphism, but the natural history and management remain unclear. Progression, regression, or persistence of terminal syringeal cavity can occur whether untethering is performed or not. Progression of the terminal syrinx occurred after tethered cord release and the enlargement of the cavity involved the entire spinal cord in the present case. Terminal syringomyelia requires close follow up for a long time even in asymptomatic cases. Surgical treatment should be considered in symptomatic cases.