A series of 37 girls with primary vesicoureteric reflux of grade II and greater severity underwent urodynamic investigations. Twenty-eight (75%) were found to have unstable bladder activity. Disordered micturition patterns were common and persisted after urinary tract infections had been eradicated. Twenty-six girls had urgency of micturition and 19 urge incontinence occurring once per week or more. The correlation between these symptoms and unstable bladder activity was significant (P less than 0.01), but there was no correlation between bladder instability and the incidence of renal scarring.