This chapter discusses the diagnosis, evaluation and management of thyroid storm. Since many disease processes can increase circulating catecholamines, and precipitation of thyroid storm is not simply sudden increase in the levels of thyroid hormones but rather an exaggerated response to internal/external stressors. Infection is the most common precipitating factor in thyroid storm. The broad clinical picture is suggestive of a hypermetabolic state with increased beta-adrenergic activity. Often more than one disease process may be occurring at once, which makes rapid identification of thyroid storm very difficult. The key is to have a high index of suspicion. Given the spectrum of illness, Burch and Wartofsky developed a scoring system to help clinically distinguish uncomplicated thyrotoxicosis from impending thyroid storm and true thyroid storm. High-output cardiac failure can be a devastating complication in thyroid storm. It is the result of excessive tachycardia and may result in pulmonary edema despite volume depletion.