After primary repair of myelomeningoceles or lipomyelomeningoceles, late progressive neurologic deterioration commonly occurs due to a treatable cause. In our experience many of these patients have a tethered cord. With early untethering, most patients are stabilized and a significant percent of the patients show improvement in their clinical status. Of 341 tethered cord releases done from 1981 to 1988, we report on 153 patients reoperated upon following primary repair. One hundred were performed after primary closure of a myelomeningocele and 53 after repair of a lipomyelomeningocele. The average age of the patients with a myelomeningocele was 6 years old, and for the spinal lipoma patients, 8 years old. The presenting symptoms were similar; weakness, deterioration in gait, scoliosis, orthopedic deformities, and urinary incontinence represented the most common complaints. All 153 patients were noted to have a tethered cord at operation. Additional pathology (dermoid tumors, hydromyelia, tight filum and diastematomyelia) was present in 30% of the cases. With the use of the CO2 laser for dissection, all but 10 patients could be untethered. Follow-up over an average of 4 years revealed 93% of the patients with a myelomeningocele had stabilization or improvement of their presenting complaints, and 7% had progression of their presenting complaints. All of the lipomyelomeningocele patients had either stabilization or improvement of their presenting complaints. There were no mortalities. Close follow-up and early treatment of this patient population is indicated. With release of the cord a significant portion of the population will have relief or improvement of their presenting complaints.