We present the clinical case of a 34-year-old male with an aneurysm of the inferior vena cava in which thrombosis led to a picture of bilateral phlegmasia cerulean dolens of the lower extremities. A clear and precise diagnosis was achieved by angio CT which allowed initial conservative management with good immediate and short term outcome. To our knowledge only 23 cases of aneurysm of the inferior vena cava have been reported in the literature worldwide making it difficult to establish a diagnostic and therapeutic algorithm for these cases. Nine cases were presented with thrombosis and in the other 14 the diagnosis was incidental. They mimic a pararenal mass requiring differential diagnosis with retroperitoneal neoplasms.