In ectopic ACTH syndrome, hypokalaemic alkalosis is typical. Ectopic ACTH is not suppressed by high doses of steroids such as 8 mg dexamethasome.

It is typically caused by small cell carcinoma of the lung. Thymoma, carcinoid tumour, medullary carcinoma of the thyroid, pancreatic carcinoma and phaeochromocytoma are associated with ectopic ACTH secretion.