Terminal syringohydromyelia is a cystic dilatation of the lower third of the spinal cord. The authors describe its incidence and characteristics, its frequent association with occult spinal dysraphism, and its clinical significance and need for surgical treatment. All 143 cases of occult spinal dysraphism treated at the Duke University Medical Center between 1972 and 1992 were reviewed. A terminal syrinx was found in 24 (27%) of the 90 cases that were evaluated by magnetic resonance (MR) imaging. In contrast, three (6.2%) of 48 cases evaluated by myelography and postmyelographic computerized tomography had a syrinx documented. The relative radiographic severity of the different syringes was estimated by using measurements of the syrinx and spinal cord on the MR images, classifying the cysts into large and small. Large syringes were frequently symptomatic, commonly presenting with pain, motor and sensory deficits of the lower extremities, scoliosis, and bowel and bladder dysfunction. Terminal syringohydromyelia with occult spinal dysraphic lesions was most often associated with tethered spinal cord from a tight filum terminale in the presence of an anorectal anomaly (67% of cases), meningocele manque (54%), and diastematomyelia (38%). An infrequent association was seen with other spinal cord anomalies. The results of surgical management of terminal syringohydromyelia were analyzed, highlighting the necessity and effectiveness of shunting the large cysts, especially in the setting of a progressive symptomatology. Of the 11 patients with shunts who underwent MR imaging, 10 showed either complete or significant resolution of the syrinx; all five patients who had presented with pain (mainly back pain) showed complete resolution of the pain after shunting; finally, one-third of patients with shunt placement had significant postoperative improvement in their neurological examination, whereas none worsened. It is stressed that terminal syringohydromyelia is an important pathological entity that should be considered in patients with occult spinal dysraphism, and treated surgically when clinically or radiographically significant.