A previously healthy 26-year-old woman presented to the emergency department complaining of a severe, throbbing, and bifrontal headache. Initial vital signs were pulse rate, 130 beats/min; blood pressure, 128/50 mm Hg; temperature, 100.1 degrees F. Shortly thereafter the patient's pulse and temperature increased to 170 beats/min and 103 degrees F, respectively. Physical examination showed a tremulous, anxious woman in moderate distress who had a diffusely and symmetrically enlarged thyroid gland. A diagnosis of thyrotoxic crisis was made, and appropriate therapy instituted, including the use of an esmolol infusion for control of hypersympathetic activity. A review of the clinical presentation, diagnosis, and management of thyrotoxic crisis is presented.