A 32‐year‐old woman was referred to our hospital because of severe psychosis and was found to have an ectopic ACTH‐producing thymic neuroendocrine tumor. Laboratory data revealed an elevated serum cortisol and plasma ACTH level, hypokalemia, and metabolic alkalosis. Chest computed tomography (CT) revealed an anterior mediastinal mass and multiple pulmonary nodules. As the patient was unable to communicate because of her consciousness disturbance, she was managed with artificial ventilation and deep sedation. Metyrapone and potassium supplementation were administered, and steroid psychosis gradually improved. Thoracic surgery was performed and the histopathological diagnosis was thymic neuroendocrine tumor with positive anti‐ACTH immunohistochemical staining. Here we present details of the case and review the literature.