Acute adrenal insufficiency is a rare disorder associated with high morbidity and mortality if allowed to progress unrecognized. A constellation of nonspecific symptoms including weakness, easy fatigue, nausea, anorexia, and weight loss are typical features of adrenal insufficiency. The index of suspicion should be particularly high if the patient has hyperpigmentation; hyponatremia and/or hyperkalemia; a history of autoimmune disease (hypothyroidism, diabetes) or recent prior use of exogenous steroids or if the patient is on anticoagulant therapy. Any decline in clinical status (hypotension, fever, decreasing mental status), especially in the setting of an acute intercurrent illness, should be treated aggressively, even before laboratory confirmation of the diagnosis. Diagnostic testing is fairly straightforward and readily available. The development of purified synthetic corticosteroid preparations has provided a safe and effective means of replacement. Early awareness, recognition, and intervention remain significant steps in altering the course of acute adrenal insufficiency.