Primary thyroid lymphoma (PTL) is a rare form of thyroid cancer that is known to be associated with Hashimoto thyroiditis. This association is supported by the presence of elevated titres of both antithyroglobulin and antimicrosomal antibodies in up to 95 percent of patients with PTL. Most patients with PTL present with a rapidly enlarging neck mass and compressive symptoms. The majority of thyroid cancer patients have normal levels of thyroid hormones; they are rarely hyperthyroid, with no obvious clinical features of thyrotoxicosis. We describe a patient who presented with minimal clinical features of thyrotoxicosis despite having markedly elevated serum free thyroxine and suppressed serum thyroid-stimulating hormone levels.