Adrenocorticotropic hormone (ACTH) and corticotropin-releasing hormone (CRH) are essential regulators of cortisol production within the hypothalamic-pituitary-adrenal (HPA) axis. Elevated cortisol levels, resulting from excessive ACTH, can lead to Cushing's syndrome, a condition with significant morbidity. Neuroendocrine tumors (NETs) can ectopically produce both ACTH and CRH, contributing to this syndrome. This review discusses the pathophysiology, types, clinical presentation, diagnosis, and management of these tumors. Emphasis is placed on the importance of identifying dual CRH/ACTH secretion, which complicates diagnosis and necessitates tailored therapeutic strategies. Furthermore, the review highlights the prognosis, common complications, and future directions for research in this area. We report the case of a 53-year-old female patient who presented with severe Cushing's syndrome and was diagnosed with ectopic ACTH syndrome. Despite initial indications pointing towards pituitary-dependent hypercortisolism, further investigations revealed the presence of a highly differentiated atypically located tumor in the upper lobe of the left lung, adjacent to the mediastinum. Immunohistochemistry of the tumor tissue demonstrated not only ACTH but also CRH and CRH-R1 expression. The simultaneous expression of these molecules supports the hypothesis of the presence of a positive endocrine feedback loop within the NET, in which the release of CRH stimulates the expression of ACTH via binding to CRH-R1. This case report highlights the challenges in diagnosing and managing ectopic ACTH syndrome, emphasizing the importance of a comprehensive diagnostic approach to identify secondary factors impacting cortisol production, such as CRH production and other contributing neuroendocrine mechanisms.