Multiple endocrine neoplasia type 1 (MEN 1) syndrome is characterized by endocrinopathies and could be associated with thymic neuroendocrine tumors (NET). On rare occasions, they can be functional adrenocorticotropic hormone-secreting thymic carcinoid leading to Cushing's syndrome. In this report, we describe a case of adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome due to a thymic NET associated with MEN type 1 syndrome. We highlight its aggressive clinical course, the premise for a high index of suspicion for an ectopic ACTH secretion, and the need for early surgical resection combined with medical therapy and alternative treatments.