© 2020 Society for Vascular SurgeryObjective: Iliocaval outflow obstruction was investigated in patients with venous ulcers caused by primary superficial disease and chronic deep vein disease Methods: After clinical assessment, patients with healed or active venous leg ulcers underwent lower extremity duplex ultrasound examination to identify the presence of venous disease in the superficial, deep and perforating systems. Bilateral contrast venography and intravascular ultrasound examination were then performed to determine the presence and degree of iliocaval obstructive lesions. Results: This retrospective study included a total of 59 patients with 71 legs presenting active or healed ulcer. There were 16 limbs (22.5%) with superficial venous reflux associated with normal infrainguinal deep veins (group I) and 55 limbs (77.5%) with infrainguinal post-thrombotic deep venous disease (group II). Using venography and intravascular ultrasound examination, the incidence of >50% of venous obstruction in the iliocaval system in groups I and II were 75% and 83.6%, respectively. All obstructive lesions in group I were nonthrombotic. However, group II included thrombotic, nonthrombotic and combinations of the two types of obstructions. Group II had more ulcers (1.73 ± 1.3 vs 1.17 ± 0.5; P =.03), larger ulcers (>6 cm in 34.1% vs 8.3%), longer duration of ulcers (71.3 ± 110.5 months vs 37.9 ± 40.4 months; P =.03), smaller diameter of refluxing superficial veins (7.7 ± 2.6 mm vs 15.1 ± 6.6 mm; P =.001), and higher incidence of occluded iliocaval systems (18 [32.7%] vs 0; P =.003) than group I. After the exclusion of bilateral cases and thrombotic obstructions, the incidence of >50% nonthrombotic obstruction in ipsilateral and contralateral sides was 76.5% and 24.4%, respectively (P =.003). Conclusions: The results of this study revealed that the majority of patients with venous ulcers with either infrainguinal primary superficial or post-thrombotic deep venous disease had an element of iliocaval venous obstruction.