In a patient already operated for abdominal aortic aneurysm fifteen months previously, because of the onset of aspecific vertigo, instrumental investigations of the supra aortic vessels showed us the presence of a non palpable mass, in the left side of the neck. Duplex Scanner, angio-CT and Angiography let us suspect the presence of an aneurysm located somewhere in the course of the thyrocervical trunk. At the operation the aneurysm, which we originally suspected to be a false and a possibly iatrogenic one, in the reality was a true aneurysm and was located at the termination of the thyrocervical trunk, just in the first segment of the inferior thyroid artery. The case is reported because of its rarity and the difficulties in the preoperative diagnosis.