Bladder, or detrusor, instability is a symptomatic condition which is characterized by uncontrollable rises in pressure within the bladder lumen leading to a feeling of urgency of micturition and, if severe enough, urinary incontinence. The rises in pressure are brought about by contraction of the detrusor smooth muscle which forms the major tissue component of the urinary bladder wall. This abnormality can be associated with a number of clinical conditions and when there is evidence of associated neurological deficits it is termed detrusor hyper-reflexia. An increase in bladder outflow resistance is also associated with detrusor instability and this is especially prevalent in men due to the age-related hypertrophy of the prostate gland which surrounds the urethra. However, in the majority of cases the cause is idiopathic and probably multifactorial. No matter what the cause, detrusor instability is one the largest causes of morbidity in the community; in the UK its prevalence increases from about 2 % in men and 9 % in women aged 15-64 years to 7 % and 12 %, respectively, in the over 65 years age group (Thomas et al. 1980; Brocklehurst, 1993).