Thyrotoxic periodic paralysis (TPP) is an uncommon but potentially lethal manifestation of hyperthyroidism characterized by muscle paralysis and hypokalemia. We have reported 3 cases of TPP in male patients, which manifested with morning muscle weakness evolved into paralysis. In all patients were found severe hypokalemia, abnormalities on electrocardiogram, and Graves' hyperthyroidism. Intravenous potassium administration led to normalization of potassium levels, and resolution of neurological symptoms. In addition, beta blockers and methimazole were started. Two patients required total thyroidectomy for poor control of hyperthyroidism with antithyroid drug. In patients presenting with periodic paralysis or diffuse muscle weakness thyroid function should be investigated in order to find out the cases secondary to unknown hyperthyroidism and to start an early appropriate combined therapy. The correct management of TPP can prevent serious cardiopulmonary complications.