Adrenal insufficiency (AI) is characterised by lack of cortisol production from the adrenal glands. This can be a primary adrenal disorder or secondary to adrenocorticotropic hormone deficiency or suppression from exogenous glucocorticoids. Symptoms of AI in children may initially be non-specific and include growth faltering, lethargy, poor feeding, weight loss, abdominal pain, vomiting and lingering illnesses. AI is treated with replacement doses of hydrocortisone. At times of physiological stress such as illness, trauma or surgery, there is an increased requirement for exogenous glucocorticoids, which if untreated can lead to an adrenal crisis and death. There are no unified guidelines for those <18 years old in the UK, leading to substantial variation in the management of AI. This paper sets out guidance for intercurrent illness, medical, dental and surgical procedures to allow timely and appropriate recognition and treatment of AI and adrenal crisis for children and young people.