The authors present a case of tumor thrombus in the inferior vena cava produced by angiomyolipoma in a young woman with tuberous sclerosis. Diagnosis was made by computed tomography (CT) by measuring the attenuation values of the tumor thrombus. The values obtained were characteristic of fat, demonstrating that tumoral invasion was the cause of the thrombus. To our knowledge, this is the first description of such an association shown by CT in the literature.