Enterocystoplasty is being used with increasing frequency in the treatment of patients with idiopathic detrusor instability. We have performed a prospective clinical and urodynamic study of this procedure in 11 patients using both conventional (CMG) and ambulatory monitoring techniques (AM). Nine of 11 patients were satisfied with the symptomatic outcome, but 7 relied on clean intermittent self-catheterisation (CISC) to achieve a good result. Urodynamic studies demonstrated a significant increase in residual urine volume from 48 +/- 72 ml before to 347 +/- 298 ml after operation, but there was only a small and statistically insignificant increase in cystometric capacity. Detrusor instability, present before operation in all patients, could still be demonstrated in over half of them after operation. However, a significant decrease in the severity of instability was found after operation as assessed by an increased volume at first unstable contraction. The bladder volume before operation at which the first unstable contraction occurred was smaller in those who still had persistent instability after enterocystoplasty compared with those in whom instability could not be identified after operation. These results suggest that all patients about to undergo ileocystoplasty should be trained in the use of CISC. In selected patients with idiopathic detrusor instability refractory to other treatment, this procedure can yield satisfactory results.