We reviewed the clinical and roentgenographic findings, treatment, and results for seventeen patients (six male and eleven female) who had segmental spinal dysgenesis, a disorder frequently confused with, but distinct from, lumbar and lumbosacral agenesis. The average age at the time of presentation to the Minnesota Spine Center or the Gillette Children's Hospital was two and a half years (range, newborn to twenty-one years), and the average duration of follow-up was eight years (range, five months to twenty-two years). At the time of the diagnosis, eight patients had neurological deficits: seven had a neurogenic bladder and four had weakness of the lower extremities. An average of 2.6 procedures (range, one to five procedures) was needed to obtain a solid fusion. Decompression of the stenotic canal was performed in ten patients, and it was followed by an improvement in neurological function in two of them. A solid fusion of the spine, arrest of the progressive kyphosis, and stabilization of neurological function were obtained in all patients. We recommend early anterior and posterior arthrodesis in patients who have segmental spinal dysgenesis, as the progressive kyphosis that inevitably develops often results in neurological deficits.