IntroductionInferior vena cava agenesis (IVCA) is one of the many anomalies of this vessel. It is one of the most uncommon anomalies, with an estimated prevalence of 0.0005–1% in the general population. Around 5% of the patients younger than 30 years with a diagnosis of deep vein thrombosis (DVT) have a total or segmental IVCA.ReportHere two unique cases of young and previously healthy male patients are reported: one with bilateral lower extremity DVT, the second with lower extremity DVT and pulmonary embolism. Both patients were found to have segmental agenesis of the inferior vena cava on computed tomography angiography (CTA). Treatment consisted of ultrasound enhanced thrombolysis (EKOS + alteplase) and venous angioplasty. Both patients were discharged with long-term (up to 24 months) oral anticoagulation and compression stockings. Follow up at 3 and 12 months revealed no new thrombotic episode.DiscussionIVCA can be asymptomatic but the majority of the symptomatic patients present with DVT. IVCA confers a risk factor for DVT. IVCA should be considered and ruled out as a rare but important risk factor and cause of DVT in previously young healthy patients. Once diagnosed, aggressive treatment must be started because of the high risk of post-thrombotic syndrome.