Segmental spinal dysgenesis is an uncommon congenital spinal defect characterized by localized segmental agenesis of the upper lumbar or thoracolumbar spine. Bony defects include significant focal canal stenosis, hypoplastic or absent vertebrae, subluxation of the spinal column, and instability. The distal bony architecture is usually normal but may be bifid. There is significant narrowing of the thecal sac and absence of adjacent nerve roots at the level of the lesion. Distal neurologic deficits are variable in severity, the prevalence of neurogenic bladder is high, and associated anomalies are common. Progressive kyphosis is inevitable. The cause is unknown, but an association with maternal diabetes and with various medications and toxins has been noted. Other authors suggested a relation to an aberrant segmental vascular supply. Treatment should be directed at the establishment and maintenance of spinal stability and arrest of the progressive kyphosis. It should consist of early anterior and posterior arthrodesis, with or without anterior decompression of the cord. Accurate visualization of this unusual deformity is difficult with conventional radiographic techniques. Three-dimensional computerized tomographic reconstruction can therefore be invaluable in preoperative planning. We report three cases of segmental spinal dysgenesis, all of which have been uniquely detailed by striking three-dimensional imaging studies.