In an attempt to create continence in myelomeningocele children we performed urethral lengthening/submucosal reimplantation, a form of bladder neck reconstruction, to create a valve allowing catheterizable access to the bladder. We present the urodynamic findings of 23 patients 4 to 89 months (mean 43.1 months) after bladder neck reconstruction and enterocytoplasty to determine the continence mechanism of this 1-way valve and characteristics of the augmented bladder. Standard cystometrograms with simultaneous pressure recording of the submucosal portion of the neourethra were undertaken with a 10F, triple lumen, urethral pressure profile catheter. Baseline pressures in the submucosal neourethra were higher than in the bladder (mean 25.3 versus 13.4 cm, water, p less than 0.001). Submucosal tunnel and bladder pressures paralleled throughout filling, with mean tunnel pressures remaining greater at the time of first (53.6 versus 45.5 cm. water, p less than 0.01) and peak (62.9 versus 55.8 cm. water, p greater than 0.05) cystoplasty contractions. Bladders augmented with detubularized ileum had fewer significant contractions (greater than 40 cm. water) than other types of cystoplasties (36% versus 92%) and over-all they had first and peak contractions at greater volumes and lesser magnitude. We conclude that continence following urethral lengthening/reimplantation results from an anatomical arrangement allowing transmission of dynamic bladder pressure changes to the submucosal neourethra and that urethral pressure exceeds bladder pressure throughout filling. Additionally, our data suggest that detubularized ileum provides a large capacity, low pressure reservoir suitable for augmentation.