This is an unusual case of a complex vascular malformation in the pelvic-inguinal region with an incidental finding of left-sided or duplicated inferior vena cava. It is possible that the pelvic-inguinal vascular malformation is post-traumatic in etiology with a history of a gunshot wound to the left thigh, as arteriovenous fistulae may develop and can remain asymptomatic for years. The duplicated inferior vena cava is a congenital variant that is an incidental finding on the only CT imaging study, and this unusual caval abnormality can present an interesting challenge in the surgical or endovascular treatment of the aforementioned complex vascular malformation.