Between September, 1989, and September, 1992, 193 infants were investigated prospectively for development of central-venous-catheter-induced thrombosis. In 25 infants intracardiac or central-venous-catheter-induced thrombosis was demonstrated (13%). A slightly higher incidence of thrombosis was found in infants with umbilical catheters in comparison with infants with subclavian catheters, although no significant difference was demonstrated. The results make clear that central venous catheters in neonatal intensive care have considerable risk in developing central venous or intracardiac thrombosis, and echocardiography is an excellent technique for diagnosing these thromboses.