Controversy exists about the timing of surgery in neonates and infants with congenital anomalies such as refluxing and/or obstructing megaureters and ectopic ureteroceles. Discussion acuminates to the fact whether or not early reconstruction causes irreversible damage to the urodynamic properties of the bladder. Between 1986 and 1992, 49 neonates and infants with obstructing or refluxing megaureters and 23 neonates and infants with ectopic ureteroceles have been operated in our hospital with a mean follow-up of 7.3 years. Reimplant surgery consisted of a modified Politano Leadbetter procedure, ureterocele surgery consisted of complete excision of the ureterocele, including the urethral part, with reconstruction of the urethra, bladder neck and bladder base combined with ureteral reimplants. Urodynamically no unexpected changes or deteriorisation have been seen in any of the patients. Bladder capacity for age, especially in the reflux group, averages 200%. Two of the ureterocele patients needed clean intermittent catheterisation for several years. Results of reflux cure in megaureter surgery were disappointing in ureters with a flat diameter between 6 and 9 mm's that were not recalibrated leading to the conclusion that in young children recalibration of the distal ureter should be done from 6 mm's upwards. No post-operative ureteral obstruction was observed in any of the cases. The conclusion is that early major reconstructions of the lower urinary tract causes no specific harm to the urodynamic properties of the bladder and pelvic floor, provided that the surgery is performed by specialised pediatric urological surgeons. The reported urodynamic problems in this patient group are probably related to lack of experience to deal with dysfunctional voiding habits that are quite common in these children, also after successful surgery. These micturation problems are not related to the surgical procedures, they are the result of pre-existing urodynamic changes of bladder function in these children.