Summary1. Hypocorticism occurring after cortisone therapy is extremely frequent, and sometimes longlasting. There is neither clinical nor biochemical sign allowing to detect its latent phase.2. Every patient having a recent (less than one year) history of intensive cortisone therapy, will not be submitted to surgery without important hormonal therapy. Cortisone treatment should never be stopped nor replaced by ACTH when emergency surgery is planned.3. Any surgical trauma supervening in a patient having been treated with cortisone will suggest acute adrenal insufficiency, and will be treated by massive administration of cortisone.4. The weekly interruption of cortisone treatment for one single injection of ACTH does not decrease the incidence of adrenal insufficiency and should accordingly be abandoned. Nevertheless, at the end of cortisone therapy, the administration of decreasing dosage of cortisone along with ACTH during 8 days, and followed by ACTH alone during 3 or 4 days seems to offer effective protection against the impending danger of functional hypocorticism.