Renal artery stenosis (RAS) is a narrowing of the arteries to one or both of the kidneys that can cause hypertension (high blood pressure) and, sometimes, reduced kidney function and size (atrophy). It occurs more commonly in older people with atherosclerosis (hardening of the arteries with plaque buildup, leading to narrowing of the channel where the blood flows). Hypertension caused by RAS is called secondary hypertension. This means that, unlike essential or primary hypertension (the most common form of high blood pressure, which does not have a specific known cause), secondary hypertension does have a specific cause. In some cases, diagnosing and treating RAS can result in decreasing or eliminating the need to take medication for hypertension. The narrowing of the kidney arteries in RAS is usually due to atherosclerosis; more rarely it can be caused by abnormal growth of tissue within the wall of the artery. The latter condition, called fibromuscular dysplasia, is potentially curable and is more common in women and younger age groups but can also occur later in life. When atherosclerosis is the cause of RAS, it is especially important to be evaluated and treated for related diseases of the heart and brain, since they are also susceptible to narrowed arteries. Atherosclerosis in those organs can lead to heart attack or stroke. The November 5, 2008, issue of JAMA includes an article about an 82-year-old woman with hypertension and renal artery stenosis.