Pre-operative knowledge of uroflowmetry and postvoiding residual urine volumes in a group of 45 women undergoing urinary incontinence surgery failed to predict risks of postoperative voiding difficulties. Only one out of nine patients needing prolonged post-operative bladder drainage (greater than or equal to 7 days) gave a pre-operative history of voiding difficulties. More than half the patients (5/9) who needed prolonged catheterization had normal flow rates were able to resume spontaneous voiding within 7 days following incontinence surgery.