A 71-year-old woman with a strong family history of thyroid cancer presented with 3 months of constipation. A carcinoid tumour of the rectum was found at colonoscopy. On physical examination, she had a large goitre and there was a 3-4 cm firm submental mass. The differential diagnosis was accessory thyroid tissue or a carcinoma metastasis. Staging computed tomography was performed to include the neck, followed by ultrasonography and aspiration biopsy of the submental mass, which confirmed the diagnosis of multinodular accessory thyroid tissue. Differences in aetiology and pathophysiology of accessory thyroid tissue and ectopic thyroid glands are discussed.