Neurofibromatosis 1 (NF1) is a common genetic disorder. Vascular abnormalities have been defined in these patients, which are usually arterial and very rarely venous. Venous aneurysms are difficult to repair as the vessel walls are friable due to the invasion of the vessel wall with neurofibromas. We present the case of a woman with NF1 who had aneurismal dilation and thrombus of the internal jugular vein. The patient was managed conservatively and died a sudden death. Venous vascular abnormalities in NF1 are rare and when present usually involve the internal jugular vein. A thrombus in the internal jugular vein in these cases is dangerous. Surgical treatment can be complicated by life-threatening haemorrhage, while conservative management can be complicated by embolization into the pulmonary circulation.