Acute adrenal insufficiency, also termed adrenal crisis, is a life-threatening endocrine emergency due to a lack of production of the adrenal hormone cortisol (and also aldosterone in primary adrenal insufficiency). Patients with both primary (PAI) and secondary adrenal insufficiency (SAI) are at risk of adrenal crisis. PAI is caused by loss of function of the adrenal gland itself resulting in both glucocorticoid and mineralocorticoid deficiency. SAI is caused by alterations in the regulation of adrenal cortisol production due to a reduction in ACTH secretion by the pituitary gland and results in glucocorticoid deficiency but maintained mineralocorticoid secretion (which is controlled by the Renin-Angiotensin-Aldosterone system). While patients with adrenal crisis due to PAI and SAI present similarly, there are some differences in presentation. Identifying patients at risk of adrenal crisis and prompt management can be lifesaving. In addition to classical causes of AI it has become increasingly evident that patients receiving exogenous glucocorticoids even as inhalers, steroid creams or nasal sprays can lead to SAI. This presentation will highlight the importance of patient and clinician education in the prevention of adrenal crisis. The presentation will also highlight the differences in presentation between PAI and SAI and discuss the optimum management of adrenal crisis.