The presence of preexisting saphenous vein lesions adversely affects graft patency. Despite careful preoperative venous duplex examination and meticulous intraoperative evaluation, clinically significant saphenous vein disease may remain undetected. We evaluated angioscopy as a means to better detect these vein lesions. Ninety saphenous vein remnants, obtained at bypass surgery, were perfusion fixed for subsequent angioscopic and histologic evaluation. The specimens were categorized by independent examiners on the basis of the angioscopic or light microscopic findings. Of the 90 vein remnants, 66 were normal by angioscopic criteria. Fifty-three (80%) of these angioscopically normal vein segments were normal histologically, and all 24 angioscopically abnormal saphenous vein remnants showed disease on microscopic examination. Angioscopy correctly identified sclerotic vein segments (n = 20) by irregular white plaques, whereas postphlebitic veins (n = 3) demonstrated multiple lumens, fibrous strands, and thickened opaque valve cusps on angioscopic evaluation. Absence of an angioscopic lumen was confirmed histologically in occluded veins (n = 2). Angioscopy failed to identify thick-walled (n = 10) and varicose (n = 2) vein segments as abnormal; one sclerotic segment was normal angioscopically, thereby lowering the sensitivity of angioscopy. Angioscopy detected unsuspected preexisting saphenous vein disease in five patients undergoing arterial reconstruction with saphenous vein. Because the use of angioscopy is a reliable means of prospectively assessing the vein for most preexisting lesions, its routine use may ultimately improve graft patency.