Multiple myeloma involving the thyroid cartilage is a very uncommon disease entity. Only 10 cases have been reported in the international literature to date and as such it constitutes a rare and challenging diagnosis to make. We report the case of a 63-year-old man with a background of malignant melanoma and multiple myeloma both of which were in remission at the time of presentation. The patient presented with hoarseness and a large neck mass that turned out to be an extramedullary deposit of his previously treated multiple myeloma indicating disease relapse. The differential diagnosis of a mass in the thyroid cartilage is discussed. Despite its rarity, this diagnosis should be considered even in patients with no history of multiple myeloma, as it can arise de-novo in the thyroid cartilage (extramedullary plasmacytoma). The importance of the multidisciplinary team (MDT) approach as well as recent advances in treatment are also discussed.