Authors of recent publications advocate central venous access by saphenous vein cutdown in the thigh. Even relatively inert SILASTIC catheters are recognized to convey a risk of large vein thrombosis when maintained for long periods. Thrombosis of the inferior vena cava (IVC) and tributaries place the patient at risk for a spectrum of problems not associated with superior vena cava (SVC) cannulation. The authors describe 46 neonatal intensive care patients with central venous cannulation of more than 2 weeks' duration. Prospective monitoring by ultrasound yielded a thrombosis rate of 16.6% for SVC cannulation and 28.5% for IVC cannulation. Complete occlusion of the IVC was clinically apparent and confirmed radiographically in four patients. In another patient, bilateral renal vein thrombosis developed, which contributed to her death. The authors compare their data for IVC and SVC cannulation and question whether the saphenous vein should be a primary route.