A 23-year-old woman had exercise-induced right leg symptoms. An extensive diagnostic workup including 2 surgical explorations was performed, but did not reveal the cause. Finally, high-resolution color-coded duplex scanning was performed, which demonstrated an isolated, nonthrombotic obstruction of the common femoral vein by a diaphragm-like membrane. Successful operative repair was accomplished with venotomy and excision of the membrane, with full relief from clinical signs and symptoms at 9-month follow-up.