Retromandibular vein aneurysm is a very rare lesion, being rarer if it is complicated by thrombosis. Due to the cervical location close to the angle of the mandible, it can simulate many pathologies. It usually presents as a soft tumor, generally asymptomatic, although it can present with pain in the event of thrombosis or nerve compression. Ultrasound is the initial diagnostic method: it allows for differentiating the solid or cystic nature of the lesion, the existence of vascularization and its connection with vascular structures. Computed tomography with intravenous contrast is the imaging method of choice, with aneurysm ligation being the treatment that offers the best results. We present the case of a patient with multiple cardiovascular risk factors in order to describe an initially asymptomatic retromandibular vein aneurysm that in its evolution was complicated by thrombosis of the aneurysm, followed by massive cerebral hemorrhage presumably caused by anticoagulation, with subsequent death.