The main aim of the study is to investigate whether taking Tolterodine for overactive bladder symptoms can reduce the thickness of the bladder wall, as measured by intra-vaginal ultrasound. This will help doctors to understand whether there is a link between changes in the thickness of the bladder wall and progression of symptoms.

Inclusion Criteria:

• Symptoms of overactive bladder (described as urinary urgency, with or without urge incontinence, usually with frequency and nocturia for more than 6 months
• Bladder wall thickness of 5mm or more

Exclusion Criteria:

• Treatment in the previous four weeks with an anticholinergic drug or any drug for the treatment of overactive bladder.
• Significant stress incontinence - Urinary tract infection or a history of intermittent urinary tract infections (more than four episodes in the last two years).
• Conditions considered significant by the investigator (e.g. cystocoele, significant bladder prolapse, bladder stone, indwelling catheter etc)