A patient is described with Cushingoid features and a tumor of the paranasal sinuses. Laboratory studies revealed hyperglycemia, hypokalemia, alkalosis, hypercortisolemia, and elevated serum ACTH levels. The cortisol level increased briskly in response to parenteral ACTH, but was only partially suppressed by dexamethasone. Microscopically, the tumor was found to be a paraganglioma containing many neurosecretory granules. Treatment with metyrapone, o, p'-DDD, and irradiation of the tumor resulted in a lasting remission. It is concluded that this unique patient suffered from Cushing's syndrome due to ectopic ACTH production by a paraganglioma of the paranasal sinuses.