Venous malformations (VM) represent vascular developmental errors. They are low-flow lesions composed of ectatic vessels that histologically and morphologically are similar to veins. Episodic thromboses commonly occur in VM. Moreover, pulmonary emboli, sudden death and chronic thromboembolic pulmonary hypertension have been described in children and adults with extensive VM. This article discusses the management and treatment of patients with extensive VM.