The acceleration of flow rate (ml/sg2) is a urodynamic parameter derived from free flow uroflowmetry. The present study was conducted to determine the role of this new parameter as an alternative to the standard filling cystometry in the diagnosis of detrusor instability in nocturnal enuresis, prostatism and female urinary incontinence. We have observed that it is not a useful parameter due to the large overlapping of the patients with unstable and normal bladder. For this reason it is not possible to establish significant predictive values.