According to the origin of the hypercortisolism, the ACTH-dependent form due to pituitary ACTH-secreting tumours is the most common form of endogenous CS in paediatric age (about 75–80% of cases), following by adrenal causes (about 15–20% of cases) including adenoma, carcinoma (which has a peak of incidence in the first decade), bilateral adrenal hyperplasia or Carney complex, with a different distribution by age. This evidence concerns the gene POMC and carcinoma.