Ischemia, induced by atherosclerosis, is a common cause of disorders in the elderly. Bladder dysfunction in older people may be caused by detrusor ischemia. We compared blood flow to the bladder and detrusor function in vivo and in vitro in young (6-month-old) and aged (24-month-old) male Sprague-Dawley rats. In both young and old rats, blood flow to the bladder measured by a laser Doppler flowmeter decreased as intravesical volume increased and was smaller in old rats than in young rats. Cystometrograms performed under anesthesia showed that old rats had smaller voiding pressure and larger bladder capacity than young rats. In isolated bladders, the pressure increase in response to bethanechol and low frequency field stimulation were impaired by aging. Volume-pressure studies showed that in isolated bladders of old rats compliance was greater and peak response to field stimulation was observed at a larger capacity. These findings indicate that bladders of older rats have a larger capacity with good compliance, but less contractility. Aging changes correlate with a decrease in blood flow to the bladder.