Aneurysm of the inferior vena cava is a rare finding in the pediatric population. We report the case of a 5-month-old infant presenting with anemia, hypertension, and dehydration in the emergency room. A renal mass was found with ultrasound and MRI and a renal tumor was first considered. Histopathologic review of the surgical specimen led to the diagnosis of aneurysmal dilatation of the vena cava.