Inferior vena cava agenesis is a rare condition and is often misdiagnosed. This anomaly is asymptomatic in the majority of cases and is usually diagnosed during imaging tests carried out for other purposes. The most frequent manifestation is deep vein thrombosis (DVT) in lower limbs and anticoagulation therapy is the most frequent treatment option. Other techniques such as thrombolysis and venous bypass are also described. We report two cases diagnosed at our institution during the last year, both of which presented with an episode of DVT. We opted for indefinite anticoagulation therapy and both patients remain asymptomatic, after 1 year of surveillance in the first case and 6 months in the second, with no new episodes of DVT. Although it is not a life-threatening anomaly, it is important to make an appropriate diagnosis and provide treatment to improve the symptoms and quality of life of these patients.