Twenty patients with 22 episodes of thyroid storm were seen between 1949 and 1969. A precipitating event, most often underlying infection, could usually be identified. The protein-bound iodine level, not previously reported in a large series of patients with thyroid storm, was significantly higher (20.8ug/100 cc) than that seen in a group of patients with uncomplicated thyrotoxicosis. Hyperglycemia was observed frequently and returned to euglycemic levels with remission of thyroid storm, a fact not heretofore emphasized. The level of consciousness and degree of mentation were valuable prognostic signs with coma indicating a more serious outcome. Improving level of consciousness and mentation were seen with a favorable response to therapy. Survival improved to 93% during the last ten years. This improvement was attributed to early diagnosis and the addition of guanethidine sulfate to the existing regimen.