PURPOSE AND MATERIALS: Out of 84 patients with meningomyelocele repaired at birth, 14 (15. 7%) children (6 boys and 8 girls, average 8.8 year-old) who underwent cord untethering for tethered cord syndrome of delayed onset (Delayed TCS) were urologically evaluated. RESULTS Eleven (78.5%) children were detected orthopedically by deterioration of lower extermities function and only 3 (21.5%) were detected urologically. Preoperative urodynamic study, however, revealed in 5 children aggravation of urinary tract dysfunction, including accelerated uninhibited contraction in 4, impaired bladder compliance in 3, decreased bladder capacity in 2 and recurrence of VUR in 1. Although there were no particular urinary symptom for detection of Delayed TCS, acceleration of uninhibited contraction seemed to be one of the most important findings. After untethering, deterioration or normalization of urological dysfunction was not seen. Six of 14 children had favorable clinical results, such as improvement of uninhibited contraction, increasing of bladder compliance and capacity, prolongation of dry time and disappearance of VUR. In 3 children Delayed TCS were detected by postoperative improvement of urinary tract function. Consequently, of 14 children who were evaluated preoperatively and postoperatively 8 (52. 7%) had urological impairment compatible with Delayed TCS. CONCLUSIONS It is not easy to detect the urological deteriorations associated with Delayed TCS behind initial neuro-urological deficits. Careful and regular follow-up examinations are required to early detection of Delayed TCS. The fact that urinary tract dysfunction improved in some cases after untethering encourages aggressive surgical untehtering of Delayed TCS.