Ectopic thyroid glands generally appear in the midline due to abnormal median migration; their presence lateral to the midline is rare. We report the case of a 42-year-old female who presented with symptoms of thyrotoxicosis and an expanding submandibular swelling. Tc-99m-sodium pertechnetate scanning showed thyroid tissue in the left submandibular region, while no thyroid tissue was seen in the normal site. The patient was treated with 10 mCi of 131I and subsequently became euthyroid. Literature review revealed seven cases of lateral aberrant thyroid tissue. The theories to explain lateral aberrant thyroid are presented.