Adrenal crises are life-threatening complications of adrenal insufficiency. These events have an estimated incidence of between 5 and 10 adrenal crises/100 patient years and are responsible for some of the increased morbidity and excess mortality experienced by patients with adrenal insufficiency. Treatment involves urgent administration of IV/IM hydrocortisone and IV fluids. Patient education regarding preventive measures, such as increasing the dose of replacement therapy (“stress dosing”) when sick, using parenteral hydrocortisone as necessary and accessing medical assistance promptly, is still considered the best approach to averting the onset of an adrenal crisis at times of physiological stress, most commonly an infection. However, recent evidence has demonstrated that patient education does not prevent many adrenal crisis events and the reasons for this are not fully understood. Furthermore, there is no widely accepted definition of an adrenal crisis. Without a validated adrenal crisis definition it is difficult to interpret variations in the incidence of adrenal crises and determine the effectiveness of preventive measures. This article aims to review the clinical aspects of adrenal crisis events, to explore the epidemiology, and to offer a definition of an adrenal crisis and to offer a perspective on future directions for research into adrenal crisis prevention. © 2016, Springer Science+Business Media New York.