We describe a 21-year-old Italian male affected by hypokalemic tetraparesis with acute onset. In the emergency ward, the patient was agitated, with tachycardia (140/min) and systolic hypertension (180/70 mm Hg). He was not able to flex the lower extremities against a light resistance and furthermore, he was hypotonic and without tendon reflexes. One hour later he developed strength deficit of the upper extremities as well. Biochemical analyses revealed severe hypopotassemia (2.1 meg/l). After administration of 140 meq potassium phosphate, the patient began to improve, and 12 h after the onset he was able to walk normally. Successive investigations documented an undiagnosed case of Graves' disease. Thyrotoxic hypokalemic paralysis has been observed almost only in Asians, however, with this case and others reported, we believe that it should be considered as a cause of muscular paralysis also in Caucasians.