High-resolution real-time ultrasonography is a simple, accurate and non-invasive method of imaging the saphenous vein preoperatively. It is useful in demonstrating areas of venous anomalies and disease, and predicts the course of the vein in the leg. Vein mapping was performed preoperatively in 100 patients undergoing coronary artery bypass operations, and ultrasonographic vein diameters and findings were correlated with those found at operation.