Split cord malformations (SCMs) may occur in conjunction with myelomeningoceles, and are often ignored or misdiagnosed, potentially causing spinal cord tethering. In this paper, we study the incidence and clinical significance of such an association. We have retrospectively reviewed the medical records and radiographs of 20 myelomeningocele patients who had a SCM. These comprised at least 6% of our myelomeningocele patients. Five of the 20 had simultaneous repair of both lesions at birth. The other 15 were diagnosed with the SCM in a delayed fashion (mean age 4.4 years). Clinical presentations that prompted a diagnostic investigation included hypertrichosis (1), pain (2), routine radiographic follow-up (2), neurourological deterioration (10) and progressive scoliosis (5). In 17 of the 20 patients, the SCM involved the placode or was within one level of it. Fifteen of these were in the area of the placode or one segment above it. Five of the 20 patients had hypertrichosis and 15 of the 20 patients had a bony midline septum (i.e. type I SCM). Several accompanying spinal dysraphic lesions also contributed to the tethering: thickened (previously inconspicuous) filum terminale (6), syringohydromyelia (5) and a neurenteric cyst with a benign teratoma (1). Arachnoiditis secondary to the prior myelomeningocele repair was found, as expected, in all 15 patients. However, in virtually all patients, there was also evidence of tethering at the level of the SCM. Long-term follow-up showed stabilization of preoperative symptoms and signs, whereas complications of the operation and clinical evidence of retethering were uncommon. Myelomeningocele patients should be screened with clinical examinations looking for hypertrichosis and with spinal radiographs preoperatively looking for evidence of SCM (bony midline septum and/or interpedicular widening not due to the myelomeningocele). Intraoperatively, the placode and the rostral spinal cord segment should be carefully inspected for an SCM and other dysraphic lesions.