Hi, Anne....I can only answer your question based on what I have read regarding this. They generally feel that at that size your chances for a rupture or dissection are greater and that at that point they will do surgery. The surgery is risky but at the measurement of 5 or greater they feel that if they don't do the surgery your risk of rupture is far greater so surgery would have to be done. I am sure someday they will come up with a far less risky type of surgery so that people can opt for surgery much sooner instead of living in limbo with these time bombs waiting to see what will happen as I am doing now. I have an aneurysm on my aortic root found in June of '05 in an incidental test..( a pre-op test for knee surgery)....Mine measures either 4 or 4.2 depending on which test I want to believe. I am due for another test this month. As of last Dec. my aneurysm had not changed since the first test, but, one never knows what is going on with their aneurysm in between tests. I hate living with this.. I am still in shock over this diagnosis. I have always taken care of myself. Only people living with aneurysms can fully understand the stress people live under having one of these monsters in their body. Have you been diagnosed with an aneurysm? Christine in Florida