Corticotroph adenomas cause ACTH oversecretion responsible for Cushing's disease. This represents the most frequent cause of Cushing's syndrome, or chronic excess of endogenous glucocorticoids. Ninety percent of corticotroph adenomas are microadenomas, sometime not visible on MRI. Corticotroph macroadenomas are rare, but can be responsible for an aggressive tumor. Cushing's disease diagnosis requires careful hormonal and imaging investigations, aiming first at the diagnosis of Cushing's syndrome and in a second step at the diagnosis of its pituitary origin. The treatment of corticotroph adenoma is mainly based on pituitary surgery. In case of failure of pituitary surgery, or in patients in whom surgery is not appropriate as a first line treatment, medical therapy (mainly anticortisolic drugs), pituitary radiotherapy or surgical bilateral adrenalectomy can be discussed.