Adrenoeorticotropichormone (ACTH) syndrome (hereinafter referred to as ectopic ACTH syndrome) is a manifestation of hypercortisolism due to abnormal secretion of ACTH by tumors other than the pituitary gland, which stimulates bilateral adrenal hyperplasia and overproduction of cortisol. Since Brown described the first case of ectopic ACTH syndrome in the world in 1928, the number of reports has gradually increased in recent years. Ectopic ACTH syndrome accounts for about 15% of cortisol disorders. There are many types of tumors that can cause ectopic ACTH secretion, the most common being small cell carcinoma of the lung (50%), thymoma (10%), pancreatic islet cell tumor (10%), bronchial carcinoid tumor (5%), but also medullary carcinoma of the thyroid, pheochromocytoma, ovarian cancer and testicular tumors. Bronchial carcinoid tumors accounted for about 41.7% of the cases in this group, which may be related to the fact that this tumor is a low-grade malignant tumor with a relatively long course, which is well recognized for its ability to manifest the typical Cushing’s syndrome. Patients with ectopic ACTH syndrome accounted for about 2.4-16% of the total number of patients with Cushing’s syndrome. Due to the lack of awareness of the disease by most clinicians, the domestic reports are lower than the foreign reports, which is also related to the fact that ectopic ACTH syndrome is difficult to diagnose because of the symptoms of Cushing’s syndrome in addition to the manifestations of the tumor itself. The prognosis of ectopic ACTH syndrome is poorer than that of cortisol disease, and the poor prognosis is related to the following reasons: (1) the malignant degree of the primary tumor is higher; (2) it is easy to be misdiagnosed, and the course of the disease is longer, and there are more complications. The clinical manifestations of ectopic ACTH syndrome can be divided into dominant and recessive. The common tumor of dominant ones is small cell carcinoma of lung, which has high degree of malignancy, rapid development of disease, large tumor volume, heavy symptoms of primary tumor, and easy to be detected by all kinds of imaging examinations. The natural course of these tumors is short, and there is not enough time to show various typical manifestations of Cushing’s syndrome. The proportion of small cell carcinoma of the lung in this group of cases is only 16.7%, which is lower than that reported in the literature, which may be related to this. However, the tumor secreted a high amount of ACTH, and if CT or ultrasound examination was performed, it could be found that bilateral adrenal hyperplasia was obvious and blood cortisol level was high. Many small cell lung cancers have a natural course of only a few months, and the diagnosis of the primary disease is not difficult, often ignoring the presence of hypercortisolism. Hypercortisolism-induced hypokalemia is often the direct cause of patient death. It is believed that the harm caused by hypercortisolism due to ectopic ACTH secreted by the tumor is far more serious than the tumor itself. Therefore, patients with small cell carcinoma of the lung should be aware of the existence of ectopic ACTH syndrome, which can be inhibited by drugs to inhibit the synthesis of ACTH, and adrenalectomy can be performed if necessary. Occult ACTH-secreting tumors have a low degree of malignancy, slow growth rate, small tumor size, and the symptoms of the primary tumor are not obvious and not easy to be detected, and some primary tumors are detected several years after the signs of Cushing’s syndrome appear. These tumors, although less malignant, have a longer course, are prone to metastasis, and hypercortisolism can cause many complications and a poor prognosis. Ectopic ACTH syndrome has a complex manifestation, with typical manifestations of Cushing’s syndrome, such as full moon face, centripetal obesity, full moon face, wide purple lines, muscle weakness and other symptoms, and combined with plasma cortisol, 24h urinary free cortisol is significantly elevated, loss of secretory rhythm, plasma ACTH is increased, none of the dexamethasone suppression test showed suppression, and all of the mephedrone tests were unresponsive, and the pituitary gland is normal in the imaging examination. Bilateral adrenal hyperplasia, it is not difficult to make a qualitative diagnosis. If the symptoms of the primary tumor are not obvious, it is more difficult to make a localized diagnosis. One-sided hyperplasia or nodular hyperplasia can be easily mistaken for adrenal lesions and misdiagnosed. The pathogenesis of ectopic ACTH syndrome is related to the APUD doctrine. Patients with laboratory tests suggesting ectopic ACTH tumors can be examined for the neural endocrine tumor sites, and chest radiographs or abdominal CT can be performed to observe the presence of small cell carcinoma of the lungs, bronchial carcinoid tumor, thymoma, pancreatic islet cell tumors, etc., and the thyroid gland, ovaries and other parts of the body can also be screened. Normal pituitary adenomas and adrenal adenomas rarely express receptors for growth inhibitors, whereas ectopic ACTH tumors often express receptors for growth inhibitors, so about 80% of patients with ectopic Cushing’s syndrome can be detected and localized by isotope-labeled orexin scans for tumors, and can be used to differentiate bilateral or unilateral adrenal hyperplasia from ectopic and orthotopic ACTH, and can be useful for tumors that are difficult to localize. It is helpful for tumors that are difficult to localize. The key to improve the treatment effect of ectopic ACTH syndrome is early diagnosis, accurate localization and radical resection of the tumor, which has a better prognosis. When the immunohistochemistry of the surgically resected specimen proves positive for ACTH and the ACTH concentration of the plasma drops to normal after surgery, the search for the source of ectopic ACTH is considered to be stopped, or else we should consider that there are also tumors in other parts of the body. Late detection, large or metastatic tumors that are difficult or pointless to resect should be treated with bilateral adrenalectomy and corticosteroid replacement therapy, which can improve the patient’s prognosis to some extent. In our group of patients who underwent bilateral adrenalectomy, there were different degrees of improvement in symptoms. For patients who refuse surgery, drugs that inhibit cortisol secretion from the adrenal cortex can be used, such as aminoglycoside, mephedrone, bis(chlorophenyl)dichloroethylene, and ketoconazole, which are effective, but the side effects are serious, and some patients can’t tolerate them. Treatment of patients with ectopic Cushing’s syndrome with octreotide, an analogue of growth inhibitors, can lead to a rapid and long-lasting reduction in tumor-secreted ACTH, which leads to a reduction in cortisol, and, in some cases, is the only effective long-term treatment, but is less well reported.