Ten cases of fatal thromboembolism after central venous catheterisation were found among the autopsies of one year. The immediate causes of death were protracted pulmonary embolism (n = 8), cerebral embolism with defect of ventricular septum (n = 1), and central regulatory disturbance following complete thrombotic occlusion of the jugular veins (n = 1). The sources of the fatal embolisms were found in thrombi in the superior vena cava, the innominate veins or subclavian veins. The relation of these thrombi to catheter-dependent lesions in the venous walls was beyond doubt. The catheters had been left in position for periods of 2 to 56 days. In 40 further autopsies with different causes of death, catheter-dependent mural lesions of varying extent were found in the venous system near the heart. Local thrombi were identified after catheterisation of not more than 24 hours. Macroscopic and microscopic appearance of these thrombi was characterised by a groove-like structure corresponding to the apposition of thrombi around the plastic catheter.