The objective of this series was to describe the findings in 2 types of iliac vein compression syndrome on intravascular ultrasonography. We conducted a retrospective review of the intravascular ultrasonographic findings in 2 patients with iliac vein compression syndrome due to 2 different types of venous spur and correlated those findings with the contrast‐enhanced venographic findings. Intravascular ultrasonography allowed differentiation of the 2 different types of iliac vein compression syndrome in analogy to the venographic classification. Both cases had compression of the left common iliac vein between the right common iliac artery and the vertebral bodies. In addition, hyperechogenic eccentric wall thickening, the presence of multiple vascular channels separated by hyperechogenic structures, and the presence of sequelae of deep venous thrombosis such as synechiae and organized thrombus can be seen on intravascular ultrasonography. The ability to perform exact measurements of the venous dimensions is an added benefit of intravascular ultrasonography. Intravascular ultrasonography can assist in the diagnosis and classification of iliac vein compression syndrome, allows assessment of its complications, and can be potentially helpful for planning endovascular treatment.