Although the use of silicone catheters for long-term central venous access is widespread, little is known about the incidence of pulmonary thromboembolic complications. We studied clinical events, lung perfusion scans, and echocardiographic screens in 34 children and adolescents with gut failure who had received cyclical parenteral nutrition for 2 months to 9 years. Major thrombosis and/or embolism was identified in 12 patients and 4 died as a consequence. Actuarial survival free from thrombosis was 53% at 5 years (95% Cl, 30-77%). Survival free from fatal pulmonary thromboembolic events was 74% at 5 years (48-99%). 3 patients required surgery to remove right atrial thrombus or pulmonary emboli. Major right atrial thrombosis and pulmonary embolism are common and potentially fatal complications of parenteral nutrition by long-term venous access in childhood. Anticoagulation is recommended.