SummaryAfter an analysis of the consequences of hypercorticism, the three causes of Cushing syndrome ate considered : adrenal tumour, paramoplasic syndrome and Cushing disease (hypereorticism of central origin).The Characteristics of hypereorticism in Cushing disease are described, as well as the changes in ACTH secretion, the anomalies of the feed-back ACTH-Cortisol system, the frequency, type and initial symptomatology of pituitary tumours. A physiopathologic concept is proposed : Cushing disease could be due to hypothalamic disturbance and primary central hypertonia of undetermined origin, responsible of pituitary stimulation, leading to adrenal hyperplasia.The created pituitary disturbance could be the site of single overactivity of micro-adenomas or of a single tumour which could make its appearance after adrenalectomy; the adrenals would show single diffuse or micro-adenomatous hyperplasia. The different histologic pictures of the pituitary or of the adrenals would constitute successive steps of a similar pathologic process.