Ectopic adrenocorticotropic hormone secretion is responsible for 12% to 17% of all cases of the Cushing syndrome. One of the most commonly described causes of ectopic adrenocorticotropic hormone secretion is small cell carcinoma of the lung. A rare cause includes a functioning neuroendocrine tumor traditionally known as carcinoids that account for 5% of all mediastinal tumors. To our knowledge, all reported cases of mediastinal carcinoids are thymic in origin and only a minority of those is functional. We present a male patient with hypertension, obstructive sleep apnea, and acid-base disorder, in whom further investigation revealed an anterior mediastinal mass and Cushing syndrome.