This case-report presents a 5-year-old girl with gastrointestinal symptoms, who became increasingly confused over the last day before admission. She was believed to be in septic shock or have meningitis and was treated with normal saline infusion, glucocorticoid and antibiotics intravenously. A few days later she was diagnosed with primary adrenal insufficiency (Morbus Addison), which is a very rare disorder among children. If untreated, the condition is lethal, and should always be considered as a differential diagnosis in severely ill patients.