Thyrotoxic periodic paralysis is an infrequent manifestation of hyperthyroidism and an uncommon cause of muscle weakness in western countries. The diagnosis should be considered in the differential when a patient presents with transient and recurrent weakness associated with hypokalaemia. We present a case of a 26-year-old Asian male presenting with sudden onset muscle weakness affecting predominantly his lower limbs on a background of weight loss. Physical examination demonstrated symmetrical proximal muscle weakness with normal sensation and reflexes. Initial biochemical investigations revealed hypokalaemia, hypomagnesaemia, and hyperthyroidism. Intravenous electrolyte replacement was administered in the emergency department. The patient's symptoms resolved during inpatient admission. Subsequent TSH receptor antibody testing and radionuclide thyroid scan confirmed a diagnosis of Graves' disease. The patient was discharged on antithyroid medication with no further episodes of weakness on follow-up. Therefore, thyrotoxic periodic paralysis can be the presenting feature of previously undiagnosed Graves' disease and should be considered in the differential diagnosis in patients presenting with weakness.