Bladder exstrophy and epispadias are congenital abnormalities of the urinary bladder. Evaluation of bladder function before and after bladder-neck reconstruction has not been done in patients with these conditions. We report the preliminary results of a prospective study of lower-urinary-tract function in 36 children (10 girls, 26 boys; age range 1.5-16 years) with bladder exstrophy and epispadias. Children's bladder function was measured by cystometry and cystography, and their upper urinary tracts were examined by ultrasound imaging. Normal bladder function was seen in children with primary epispadias but this was severely impaired in children who had had conventional bladder-neck surgery for continence, implying that this may not be the optimal treatment. Contrary to current assumption, children with closed exstrophy bladders are not capable of normal function, and the abnormalities we identified may be a major cause of upper-urinary-tract damage and may impair development of bladder capacity. Although unrecognised in the past, involuntary bladder contractions are a primary cause of urine leakage persisting in children with exstrophy and epispadias after continence surgery. Detailed functional testing should become a routine part of the evaluation of children with exstrophy and epispadias.