Purpose The purpose of this study was to identify risk factors and evaluate clinical outcomes associated with incidental left common iliac vein compression on CT imaging. Methods This is a retrospective study that reviewed venous-phase abdomen and pelvis CT scans to identify patients with incidental extrinsic compression of the left common iliac vein due to an overlying right common iliac artery. A total of 726 patients were included (364 females, 362 males; mean patient age: 61.9 ± 15.9 years). Board-certified radiologists reviewed all CT scans. Significant left iliac vein compression was defined as >50% luminal narrowing. Results Significant iliac vein compression was identified in 114 (15.7%) patients and was more common in females (19.5%) versus males (11.9%) ( p < 0.01). Patients with iliac vein compression >50% had significantly lower BMI than those without compression (24.8 ± 6.2 vs 28.7 ± 7.2 kg/m 2 , p < 0.01). Patients with incidental left iliac vein compression had a higher rate of prior left lower extremity DVT ( p = 0.02). Conclusion Incidental left common iliac vein compression was present in approximately 16% of patients and was more frequent among females. Compression was associated with lower BMI and more than twice the rate of ipsilateral DVT, despite no prior diagnosis of MTS. These findings suggest that incidental iliac vein compression could have more clinical significance than previously recognized.