Two patients developed superior vena cava syndrome following total parenteral nutrition through a central venous catheter. Infection may have contributed to the development of the thromboses. In one patient a "sleeve thrombus" probably fragmented when the catheter was withdrawn, leading to multiple pulmonary embolisms. The other patient had a mural thrombosis with complete occlusion of the superior vena cava. In view of the potentially high mortality of this serious complication, early diagnosis and treatment are essential.