It's known that benign prostatic hypertrophy arise from the glands that surround the proximal prostatic urethra. In these cases voiding disorders may be due by detrusor instability alone or associated with cervical urethral obstruction. At first Griffiths and Schafer and subsequently Sarky have introduced some correlations that are able to differentiate the bladder outlet obstruction from the impaired detrusor contractility. On the contrary with regard to the behaviour of detrusor during obstruction, in connection with histological findings, several interpretations have been expressed. The theory more credited has been expressed by Gosling who has showed a reduction of the parasympathetic innervation of detrusor and consequent hypersensitivity due to denervation.