A range of hormonal manipulations have been proposed as adjunctive therapy during critical care. These therapies might be used to treat a pre-existing or acquired hormonal disorder. Additionally, hormonal manipulation has been suggested to alter the long-term outcome of critical illness, even in patients without structural abnormalities of endocrine glands. Currently, the effectiveness of these anabolic therapies has not been established and they might be harmful in some patient groups. Recently, it has been recognized that many critically-ill patients have low levels of vitamin D and this is associated with an adverse outcome. It is still unclear whether replacement of vitamin D will be effective in improving outcome. This chapter will also highlight the importance of recognizing and addressing hormonal deficiency in patients with known pituitary disease and with traumatic brain injury (TBI). TBI is associated with a high prevalence of acute and long-term pituitary dysfunction. The management of the rare, but important thyroid disorders requiring critical care, thyroid storm, and myxoedema coma, will also be discussed.