SUMMARYSeven cases of adrenocortical hyperfunction associated with ACTH secreting carcinoid tumours of lung are reported. The clinical manifestations, laboratory investigations and treatment are compared with twenty‐one similar cases already recorded. The clinical picture of this disorder shows features of both pituitary dependent Cushing's syndrome and of the ectopic ACTH syndrome associated with carcinoma of lung. The problems of accurate diagnosis are described. The effects of treatment, both surgical and medical, of the adrenocortical hyperfunction are described and the problems of identifying and removing the carcinoid tumour are discusse