72-year-old male patient with 3 left lower extremity DVTs. The patient was developing severe post-thrombotic syndrome (PTS). The patient was positive for Lupus anticoagulant was being treated with oral anticoagulation. Apart from a lower extremity venous ultrasound, no investigation of the pelvic venous system was done. Imaging of the venous outflow in the abdomen and pelvis showed severe compression of the left external iliac vein. Intravascular ultrasound confirmed the compression. Treatment with stenting and venoplasty was performed. The patient’s symptoms of PTS improved. Had the patient been treated earlier, they would have had a better long-term outcome. Patients with recurrent DVT or with unprovoked DVT should be evaluated for iliac vein compression.