A 22-year-old woman with a newly detected chondroid liposarcoma located in the iliac muscle was diagnosed as having bilateral pulmonary embolism. Gadolinium-enhanced MRI further revealed a long distance thrombus reaching from the iliac vein to the right atrium. The thrombus was attributed to a hypercoagulability state which has been described for chondroid liposarcoma. High-dose chemotherapy with autologous stem cell support reduced the tumor burden and led to a symptom-free interval of 6 months. Despite therapeutic anticoagulation, repeated imaging showed no reduction or remodeling of the thrombus. However, when the thrombus progressed again, the patient underwent cardiac surgery and histology revealed the intravascular growth of the known chondroid liposarcoma. We conclude that in sarcoma patients intravascular tumor growth must be kept in mind when imaging is suggestive for thrombosis.